Sulfonate salts and derivatives, photoacid generators, resist compositions, and patterning process

ABSTRACT

Sulfonate salts have the formula: CF 3 —CH(OH)—CF 2 SO 3   − M +  wherein M +  is a Li, Na, K, ammonium or tetramethylammonium ion. Because of inclusion within the molecule of a hydroxyl group which is a polar group, the sulfonic acids are effective for restraining the length of acid diffusion through hydrogen bond or the like. The photoacid generators that generate these sulfonic acids perform well during the device fabrication process including coating, pre-baking, exposure, post-exposure baking, and developing steps. The photoacid generators are little affected by water left on the wafer during the ArF immersion lithography.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2005-316156 filed in Japan on Oct. 31, 2005, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to photoacid generators, resist compositions comprising the same, and a patterning process using the same. More particularly, it relates to novel sulfonate salts and derivatives thereof suitable for use as photoacid generators for resist compositions.

BACKGROUND OF THE INVENTION

While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, DUV and VUV lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using an ArF excimer laser as the light source is thought requisite to the micropatterning technique capable of achieving a feature size of 0.13 μm or less.

The ArF lithography started partial use from the fabrication of 130-nm node devices and became the main lithography since 90-nm node devices. Although lithography using F₂ laser (157 nm) was initially thought promising as the next lithography for 45-nm node devices, its development was retarded by several problems. A highlight was suddenly placed on the ArF immersion lithography that introduces a liquid having a higher refractive index than air (e.g., water, ethylene glycol, glycerin) between the projection lens and the wafer, allowing the projection lens to be designed to a numerical aperture (NA) of 1.0 or higher and achieving a higher resolution. See Journal of Photopolymer Science and Technology, Vol. 17, No. 4, p587 (2004).

In the photolithography using an ArF excimer laser (wavelength 193 nm) as the light source, a high sensitivity resist material capable of achieving a high resolution at a small dose of exposure is needed to prevent the degradation of precise and expensive optical system materials. Among several measures for providing high sensitivity resist material, the most common is to select each component which is highly transparent at the wavelength of 193 nm. For example, polyacrylic acid and derivatives thereof, norbornene-maleic anhydride alternating copolymers, polynorbornene, ring-opening metathesis polymers, and hydrogenated ring-opening metathesis polymers have been proposed as the base resin. This choice is effective to some extent in that the transparency of a resin alone is increased.

Studies have also been made on photoacid generators. In prior art chemically amplified resist compositions for lithography using KrF excimer laser, photoacid generators capable of generating alkane- or arene-sulfonic acid are used. However, the use of these photoacid generators in chemically amplified resist compositions for ArF lithography results in an insufficient acid strength to scissor acid labile groups on the resin, a failure of resolution or a low sensitivity. Thus these photoacid generators are not suited for the microfabrication of microelectronic devices.

For the above reason, photoacid generators capable of generating perfluoroalkanesulfonic acid having a high acid strength are generally used in ArF chemically amplified resist compositions. These photoacid generators capable of generating perfluoroalkanesulfonic acid have already been developed for use in the KrF resist compositions. For instance, JP-A 2000-122296 and U.S. Pat. No. 6,048,672 (or JP-A 11-282168) describe photoacid generators capable of generating perfluorohexanesulfonic acid, perfluorooctanesulfonic acid, perfluoro-4-ethylcyclohexanesulfonic acid, and perfluorobutanesulfonic acid. JP-A 2002-214774, U.S. Patent Application Publication 2003-0113659 A1 (JP-A 2003-140332), and U.S. Patent Application Publication 2002-0197558 A1 describe novel photoacid generators capable of generating perfluoroalkyl ether sulfonic acids.

On the other hand, perfluorooctanesulfonic acid and homologues thereof (collectively referred to as PFOS) are considered problematic with respect to their stability (or non-degradability) due to C-F bonds, and biological concentration and accumulation due to hydrophobic and lipophilic natures. The US EPA adopted Significant New Use Rule, listing 13 PFOS-related chemical substances and further listing 75 chemical substances although their use in the photoresist field is excluded. See Federal Register/Vol. 67, No. 47, page 11008/Monday, Mar. 11, 2002, and Federal Register/Vol. 67, No. 236, page 72854/Monday, Dec. 9, 2002.

Facing the PFOS-related problems, manufacturers made efforts to develop partially fluorinated alkane sulfonic acids having a reduced degree of fluorine substitution. For instance, JP-A 2004-531749 describes the development of α,α-difluoroalkanesulfonic acid salts from α,α-difluoroalkene and a sulfur compound and discloses a resist composition comprising a photoacid generator which generates such sulfonic acid upon irradiation, specifically di(4-tert-butylphenyl)iodonium 1,1-difluoro-1-sulfonate-2-(1-naphthyl)ethylene. JP-A 2004-2252 describes the development of α,α,β,β-tetrafluoroalkanesulfonic acid salts from α,α,β,β-tetrafluoro-α-iodoalkane and sulfur compound and discloses a photoacid generator capable of generating such a sulfonic acid and a resist composition comprising the same. JP-A 2004-307387 discloses 2-(bicyclo[2.2.1]hept-2-yl)-1,1-difluoroethanesulfonic acid salts and a method of preparing the same. Furthermore, JP-A 2005-266766 discloses a photosensitive composition comprising a compound capable of generating a partially fluorinated alkane sulfonic acid having a sulfonylamide structure derived from perfluoroalkylene sulfonyl difluoride.

The substances disclosed in these patents have a reduced degree of fluorine substitution, but suffer from several problems. They have giant hydrocarbon skeletons which are unsusceptible to degradation. A certain limit is imposed on the molecular design for changing the size of alkanesulfonic acid. The starting materials containing fluorine are expensive.

With respect to the immersion lithography, there remain some problems. Minute water droplets are left on the resist and wafer after the immersion exposure, which can often cause damages and defects to the resist pattern profile. The resist pattern after development can collapse or deform into a T-top profile. There exists a need for a patterning process which can form a satisfactory resist pattern after development according to the immersion lithography.

DISCLOSURE OF THE INVENTION

The photoacid generator (PAG) produces an acid which must satisfy many requirements including a sufficient acid strength to cleave acid labile groups in a resist material, an adequate diffusion in the resist material, low volatility, minimal dissolution in water, no foreign matter left after development and resist removal, and good degradability in that it is decomposed away after the expiration of its role in lithography without imposing a load to the environment. No acids produced by prior art PAGs satisfy these requirements.

An object of the invention is to provide sulfonate salts and derivatives thereof which have solved the problems of prior art photoacid generators, and especially are improved in resolution and pattern profile in conjunction with the ArF lithography, and are thus suitable as a photoacid generator in resist material. Another object is to provide a photoacid generator, a resist composition, and a patterning process.

The inventors have found that by starting with 1,1,1,3,3,3-hexafluoro-2-propanol which is readily available in the industry, deriving therefrom substituted or unsubstituted aliphatic or aromatic carboxylic acid esters of 1,1,3,3,3-pentafluoropropen-2-yl, and reacting the esters with sulfur compounds such as sodium sulfite and sodium hydrogen sulfite, there are formed 1,1,3,3,3-pentafluoro-2-acyloxypropane-1-sulfonate salts; that compounds which are obtained by preparing intermediates, typically onium salts, oxime sulfonates and sulfonyloxyimides from these sulfonate salts, followed by hydrolysis of the resulting esters are effective photoacid generators in chemically amplified resist compositions. The present invention is predicated on this finding.

The present invention provides sulfonate salts, derivatives thereof, photoacid generators, resist compositions and a patterning process, defined below.

-   [1] A sulfonate salt having the general formula (1a):     CF₃—CH(OH)—CF₂SO₃ ⁻M⁺  (1a)     wherein M⁺ is a lithium, sodium, potassium, ammonium or     tetramethylammonium ion. -   [2] A photoacid generator for chemically amplified resist     compositions which generates a sulfonic acid upon exposure to     high-energy radiation selected from UV, deep-UV, electron beam,     x-ray, excimer laser, gamma-ray and synchrotron radiation, said     sulfonic acid having the general formula (1):     CF₃—CH(OH)—CF₂SO₃ ⁻H⁺  (1). -   [3] A sulfonium salt having the general formula (2):     R¹R²R³S⁺CF₃—CH(OH)—CF₂SO₃ ⁻  (2)     wherein R¹, R² and R³ are each independently a substituted or     unsubstituted, straight or branched C₁-C₁₀ alkyl, alkenyl or     oxoalkyl group, or a substituted or unsubstituted C₆-C₁₈ aryl,     aralkyl or aryloxoalkyl group, or any two or more of R¹, R² and R³     may bond together to form a ring with the sulfur atom. -   [4] A sulfonium salt having the general formula (2a):     (R⁴—(O)_(n))_(m)-PhS⁺Ph₂CF₃—CH(OH)—CF₂SO₃ ⁻  (2a)     wherein R⁴ is a substituted or unsubstituted, straight, branched or     cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or     unsubstituted C₆-C₁₄ aryl group, Ph is phenyl, m is 1 to 5, and n is     0 or 1. -   [5] A iodonium salt having the general formula (2b):     R⁴—(O)_(n)-PhI⁺Ph(O)_(n)—R⁴CF₃—CH(OH)—CF₂SO₃ ⁻  (2b)     wherein R⁴, Ph and n are as defined above. -   [6] A N-sulfonyloxyimide compound having the general formula (3a):

wherein X and Y are each independently hydrogen or a substituted or unsubstituted C₁-C₆ alkyl group, or X and Y may bond together to form a saturated or unsaturated C₆-C₁₂ ring with the carbon atoms to which they are attached, and Z is a single bond, double bond, methylene group or oxygen atom.

-   [7] An oxime sulfonate compound having the general formula (3b):

wherein q is 0 or 1; p is a single bond, a substituted or unsubstituted C₁-C₂₀ alkyl group or a substituted or unsubstituted C₆-C₁₅ aryl group when q is 0; or p is a substituted or unsubstituted C₁-C₂₀ alkylene group or a substituted or unsubstituted C₆-C₁₅ arylene group when q is 1; EWG is a cyano, trifluoromethyl, perfluoroethyl, perfluoropropyl, 5H-perfluoropentyl, 6H-perfluorohexyl, nitro or methyl group, and when q is 1, two EWG's may bond together to form a ring of 6 carbon atoms with the carbon atoms to which they are attached.

-   [8] A resist composition comprising a base resin, an acid generator,     and a solvent, said acid generator comprising a photoacid generator     which generates a sulfonic acid having formula (1) as set forth in     [2]. -   [9] The resist composition of [8], wherein said base resin is at     least one polymer selected from the group consisting of     poly(meth)acrylic acid and derivatives thereof, alternating     copolymers of a cycloolefin derivative and maleic anhydride,     copolymers of ternary or more components comprising a cycloolefin     derivative, maleic anhydride, and polyacrylic acid or derivatives     thereof, cycloolefin derivative-α-trifluoromethyl acrylate     copolymers, polynorbornene, ring-opening metathesis polymers, and     hydrogenated ring-opening metathesis polymers. -   [10] The resist composition of [8], wherein said base resin is a     polymeric structure containing silicon atoms. -   [11] The resist composition of [8], wherein said base resin is a     polymeric structure containing fluorine atoms. -   [12] A chemically amplified positive resist composition comprising a     base resin as set forth in [9], [10] or [11], a photoacid generator     which generates a sulfonic acid having formula (1) as set forth in     [2], and a solvent, wherein said base resin is insoluble or     substantially insoluble in a liquid developer, and becomes soluble     under the action of the acid. -   [13] The chemically amplified positive resist composition of [12],     further comprising a basic compound. -   [14] The chemically amplified positive resist composition of [12] or     [13], further comprising a dissolution inhibitor. -   [15] A process for forming a pattern comprising the steps of     applying the resist composition of any one of [8] to [14] onto a     substrate to form a coating; heat treating the coating and exposing     it to high-energy radiation having a wavelength of up to 300 nm     through a photomask; and optionally heat treating and developing the     exposed coating with a developer. -   [16] The process of [15], wherein the exposing step relies on     immersion lithography comprising directing radiation from an ArF     excimer laser having a wavelength of 193 nm through a projection     lens, with a liquid such as water, glycerin or ethylene glycol     intervening between the coated substrate and the projection lens.

BENEFITS OF THE INVENTION

The sulfonic acids of the invention are effective for restraining the length of acid diffusion to an appropriate extent through hydrogen bond or the like because of inclusion within the molecule of a hydroxyl group which is a polar group. The photoacid generators that generate these sulfonic acids perform well without raising problems during the device fabrication process including coating, pre-baking, exposure, post-exposure baking, and developing steps. The photoacid generators are little affected by water left on the wafer during the ArF immersion lithography, restraining defects. The sulfonic acids are very useful synthesis intermediates because they can be converted, through reaction with acid halides, acid anhydrides or alkyl halides, to those having bulkier functional groups such as acyl and alkyl groups. Additionally, due to a low molecular weight and the inclusion of a hydrophilic group, the sulfonic acids are less accumulative in the human body. In the disposal by combustion, the sulfonic acids are more combustible because of a low degree of fluorine substitution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the ¹H-NMR/DMSO-d₆ spectrum of PAG1 in Synthesis Example 11.

FIG. 2 is a diagram showing the ¹⁹F-NMR/DMSO-d₆ spectrum of PAG1 in Synthesis Example 11.

FIG. 3 is a diagram showing the ¹H-NMR/DMSO-d₆ spectrum of PAG2 in Synthesis Example 12.

FIG. 4 is a diagram showing the ¹⁹F-NMR/DMSO-d₆ spectrum of PAG2 in Synthesis Example 12.

FIG. 5 is a diagram showing the ¹⁹F-NMR/D₂O spectrum of Anion 1 in Synthesis Example 19.

FIG. 6 is a diagram showing the ¹H-NMR/DMSO-d₆ spectrum of PAG9 in Reference Example 1.

FIG. 7 is a diagram showing the ¹⁹F-NMR/DMSO-d₆ spectrum of PAG9 in Reference Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The notation (Cn-Cm) means a group containing from n to m carbon atoms per group.

Sulfonate Salt

The sulfonate salt of the invention has the general formula (1a): CF₃—CH(OH)—CF₂SO₃ ⁻M⁺  (1a) wherein M⁺ is a lithium, sodium, potassium, ammonium or tetramethylammonium ion.

For simplicity of synthesis and ease of isolation, only lithium, sodium, potassium, ammonium and tetramethylammonium salts are specified herein as the sulfonate salt. Nevertheless, salts of divalent cations like calcium and magnesium salts and organic amine salts are also acceptable. No particular limit is imposed on sulfonate salts as long as they can exist as stable salts.

Photoacid Generator

The photoacid generators of the invention, which are typically in the form of sulfonium salts, iodonium salts, oxime sulfonates and sulfonyloxyimides, are sensitive to high-energy radiation such as UV, deep-UV, electron beam, x-ray, excimer laser, gamma-ray and synchrotron radiation and generate sulfonic acids having the general formula (1): CF₃—CH(OH)—CF₂SO₃ ⁻H⁺  (1) upon exposure thereto. They are thus useful as photoacid generators in chemically amplified resist compositions. Sulfonium Salt

The sulfonium salt of the invention has the general formula (2):

wherein R¹, R² and R³ are each independently a substituted or unsubstituted, straight or branched C₁-C₁₀ alkyl, alkenyl or oxoalkyl group, or a substituted or unsubstituted C₆-C₁₈ aryl, aralkyl or aryloxoalkyl group, or any two or more of R¹, R² and R³ may bond together to form a ring with the sulfur atom.

In formula (2), R¹, R² and R³ are each independently selected from among substituted or unsubstituted, straight or branched C₁-C₁₀ alkyl, alkenyl and oxoalkyl groups, and substituted or unsubstituted C₆-C₁₈ aryl, aralkyl and aryloxoalkyl groups, or any two or more of R¹, R² and R³ may bond together to form a ring with the sulfur atom. Suitable alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl. Suitable alkenyl groups include vinyl, allyl, propenyl, butenyl, hexenyl, and cyclohexenyl. Suitable oxoalkyl groups include 2-oxocyclopentyl, 2-oxocyclohexyl, 2-oxopropyl, 2-oxoethyl, 2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and 2-(4-methylcyclohexyl)-2-oxoethyl. Suitable aryl groups include phenyl, naphthyl, and thienyl; 4-hydroxyphenyl; alkoxyphenyl groups such as 4-methoxyphenyl, 3-methoxyphenyl, 2-methoxyphenyl, 4-ethoxyphenyl, 4-tert-butoxyphenyl, and 3-tert-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and 2,4-dimethylphenyl; alkylnaphthyl groups such as methylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such as methoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such as dimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups such as dimethoxynaphthyl and diethoxynaphthyl. Suitable aralkyl groups include benzyl, 1-phenylethyl and 2-phenylethyl. Suitable aryloxoalkyl groups include 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl, 2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl. When two or more of R¹, R² and R³ bond together to form a ring structure with the sulfur atom, 1,4-butylene and 3-oxa-1,5-pentylene are exemplary of each. Also included are aryl groups having polymerizable substituent radicals such as acryloyloxy and methacryloyloxy radicals, examples of which are 4-(acryloyloxy)phenyl, 4-(methacryloyloxy)phenyl, 4-(acryloyloxy)-3,5-dimethylphenyl, 4-(methacryloyloxy)-3,5-dimethylphenyl, 4-vinyloxyphenyl, and 4-vinylphenyl groups.

Illustrative examples of the sulfonium cation include triphenylsulfonium, (4-tert-butoxyphenyl)diphenylsulfonium, bis(4-tert-butoxyphenyl)phenylsulfonium, tris(4-tert-butoxyphenyl)sulfonium, (3-tert-butoxyphenyl)diphenylsulfonium, bis(3-tert-butoxyphenyl)phenylsulfonium, tris(3-tert-butoxyphenyl)sulfonium, (3,4-di-tert-butoxyphenyl)diphenylsulfonium, bis(3,4-di-tert-butoxyphenyl)phenylsulfonium, tris(3,4-di-tert-butoxyphenyl)sulfonium, diphenyl(4-thiophenoxyphenyl)sulfonium, (4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium, tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium, (4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium, tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium, dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium, 4-methoxyphenyldimethylsulfonium, trimethylsulfonium, 2-oxocyclohexylcyclohexylmethylsulfonium, trinaphthylsulfonium, tribenzylsulfonium, diphenylmethylsulfonium, dimethylphenylsulfonium, 2-oxo-2-phenylethylthiacyclopentanium, diphenyl-2-thienylsulfonium, 4-n-butoxynaphthyl-1-thiacyclopentanium, 2-n-butoxynaphthyl-1-thiacyclopentanium, 4-methoxynaphthyl-1-thiacyclopentanium, and 2-methoxynaphthyl-1-thiacyclopentanium. Preferred cations are triphenylsulfonium, 4-tert-butylphenyldiphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium, tris(4-tert-butylphenyl)sulfonium, and (4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium.

Also included are (4-methacryloyloxyphenyl)diphenylsulfonium, (4-acryloyloxyphenyl)diphenylsulfonium, (4-methacryloyloxy-3,5-dimethylphenyl)diphenylsulfonium, (4-acryloyloxy-3,5-dimethylphenyl)diphenylsulfonium, (4-methacryloyloxyphenyl)dimethylsulfonium, (4-acryloyloxyphenyl)dimethylsulfonium, and the like. For these polymerizable sulfonium cations, reference may be made to JP-A 4-230645 and JP-A 2005-84365. These polymerizable sulfonium salts may be used as a monomer in forming a polymer to be described later.

Another embodiment is a sulfonium salt having the general formula (2a):

wherein R⁴ is a substituted or unsubstituted, straight, branched or cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or unsubstituted C₆-C₁₄ aryl group, m is 1 to 5, and n is 0 or 1.

In formula (2a), R⁴ is as defined above, the subscript m is an integer of 1 to 5, and n is 0 or 1. The substitution position of R⁴—(O)_(n)— group is not particularly limited, but is preferably 4- or 3-position on the phenyl group, and more preferably 4-position. Examples of groups represented by R⁴ include methyl, ethyl, n-propyl, sec-propyl, cyclopropyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-octyl, n-decyl, n-dodecyl, trifluoromethyl, phenyl, 4-methoxyphenyl, and 4-tert-butylphenyl. In the case of n=1, acryloyl, methacryloyl, vinyl, and allyl are exemplary of R⁴.

Illustrative examples of the sulfonium cation include 4-methylphenyldiphenylsulfonium, 4-ethylphenyldiphenylsulfonium, 4-tert-butylphenyldiphenylsulfonium, 4-cyclohexylphenyldiphenylsulfonium, 4-n-hexylphenyldiphenylsulfonium, 4-n-octylphenyldiphenylsulfonium, 4-methoxyphenyldiphenylsulfonium, 4-ethoxyphenyldiphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium, 4-cyclohexyloxyphenyldiphenylsulfonium, 4-n-hexyloxyphenyldiphenylsulfonium, 4-n-octyloxyphenyldiphenylsulfonium, 4-dodecyloxyphenyldiphenylsulfonium, 4-trifluoromethylphenyldiphenylsulfonium, 4-trifluoromethyloxyphenyldiphenylsulfonium, 4-tert-butoxycarbonylmethyloxyphenyldiphenylsulfonium, (4-methacryloyloxyphenyl)diphenylsulfonium, (4-acryloyloxyphenyl)diphenylsulfonium, (4-methacryloyloxy-3,5-dimethylphenyl)diphenylsulfonium, (4-acryloyloxy-3,5-dimethylphenyl)diphenylsulfonium, (4-methacryloyloxyphenyl)dimethylsulfonium, and (4-acryloyloxyphenyl)dimethylsulfonium.

Iodonium Salt

A further embodiment of the invention is a iodonium salt having the general formula (2b):

wherein R⁴ is a substituted or unsubstituted, straight, branched or cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or unsubstituted C₆-C₁₄ aryl group, and n is 0 or 1.

In formula (2b), R⁴ is as defined above. The substitution position of R⁴—(O)_(n)— group is not particularly limited, but is preferably 4- or 3-position on the phenyl group, and more preferably 4-position.

Illustrative examples of the iodonium cation include bis(4-methylphenyl)iodonium, bis(4-ethylphenyl)iodonium, bis(4-tert-butylphenyl)iodonium, bis(4-(1,1-dimethylpropyl)phenyl)iodonium, 4-methoxyphenylphenyliodonium, 4-tert-butoxyphenylphenyliodonium, 4-acryloyloxyphenylphenyliodonium, and 4-methacryloyloxyphenylphenyliodonium, with the bis(4-tert-butylphenyl)iodonium being preferred.

N-Sulfonyloxyimide

A further embodiment of the invention is a N-sulfonyloxyimide compound having the general formula (3a):

wherein X and Y are each independently hydrogen or a substituted or unsubstituted C₁-C₆ alkyl group, or X and Y may bond together to form a saturated or unsaturated C₆-C₁₂ ring with the carbon atoms to which they are attached; and Z is a single bond, double bond, methylene group or oxygen atom.

Illustrative examples of the imide skeleton excluding the sulfonate moiety are given below. For the imide skeleton, reference may be made to JP-A 2003-252855.

Oxime Sulfonate

A further embodiment of the invention is an oxime sulfonate compound having the general formula (3b):

wherein q is 0 or 1; p is a single bond, a substituted or unsubstituted C₁-C₂₀ alkyl group or a substituted or unsubstituted C₆-C₁₅ aryl group when q is 0; or p is a substituted or unsubstituted C₁-C₂₀ alkylene group or a substituted or unsubstituted C₆-C₁₅ arylene group when q is 1. EWG is a cyano, trifluoromethyl, perfluoroethyl, perfluoropropyl, 5H-perfluoropentyl, 6H-perfluorohexyl, nitro or methyl group, and when q is 1, two EWG's may bond together to form a ring of 6 carbon atoms with the carbon atoms to which they are attached.

The skeletons of these oxime sulfonates are described in U.S. Pat. No. 6,261,738, JP-A 9-95479, JP-A 9-208554, JP-A 9-230588, Japanese Patent No. 2,906,999, JP-A 9-301948, JP-A 2000-314956, JP-A 2001-233842, and International Publication 2004-074242.

Exemplary skeletons of oxime sulfonates excluding the sulfonate moiety are given below.

Described below is how to synthesize the sulfonium salts, iodonium salts, oxime sulfonates or sulfonyloxyimides capable of generating sulfonic acids having formula (1).

Synthesis may be carried out by starting with 1,1,3,3,3-pentafluoropropen-2-yl aliphatic or aromatic carboxylate esters, typically 1,1,3,3,3-pentafluoropropen-2-yl benzoate, which were developed by Nakai et al. using 1,1,1,3,3,3-hexafluoro-2-propanol as the starting reactant (see Tetrahedron Lett., Vol. 29, 4119 (1988)), and reacting the esters with sodium hydrogen sulfite or sodium sulfite in the presence of a radical initiator such as azobisisobutyronitrile or benzoyl peroxide in a solvent which is water or alcohol or a mixture thereof, thereby synthesizing 2-acyloxy-1,1,3,3,3-pentafluoropropane-1-sulfonic acid salts. See R. B. Wagner et al., Synthetic Organic Chemistry, pp. 813-814, John Wiley & Sons, Inc. (1965). The foregoing sulfonic acid salts may be converted into sulfonium salts or iodonium salts by ordinary anion exchange reaction.

The onium salts can be synthesized in accordance with the teachings of The Chemistry of Sulfonium Group Part 1, John-Wiley & Sons (1981), Advanced Photochemistry, Vol. 17, John-Wiley & Sons (1992), J. Org. Chem., 53, 5571-5573, 1988, JP-A 8-311018, JP-A 9-15848, JP-A 2001-122850, JP-A 7-25846, JP-A 2001-181221, JP-A 2002-193887, and JP-A 2002-193925.

The onium cation having an acryloyloxy or methacryloyloxy group as the polymerizable substituent group can be synthesized by reacting (currently available) hydroxyphenyldiphenylsulfonium halide with acryloyl chloride or methacryloyl chloride under basic conditions according to the methods described in JP-A 4-230645 and JP-A 2005-84365.

Anion exchange may be performed in an alcohol solvent such as methanol or ethanol or a two-layer system of dichloromethane and water or the like. Alternatively, anion exchange may be performed by another recipe of reacting a corresponding methyl sulfonate with sulfonyl halide or iodonium halide, and removing the halide ion as methyl halide, as taught in JP-A 2002-167340.

Also, the imide sulfonate or oxime sulfonate can be synthesized by reacting the sulfonate salt with a chlorinating agent such as thionyl chloride, phosphorus oxychloride or phosphorus pentachloride to form a corresponding sulfonyl chloride or sulfonic acid anhydride, and further reacting with N-hydroxydicarboxylimide or oxime in a conventional way. For the synthesis of imide sulfonate or oxime sulfonate, reference should be made to the above-cited JP-A 2003-252855, U.S. Pat. No. 6,261,738, JP-A 9-95479, JP-A 9-208554, JP-A 9-230588, Japanese Patent No. 2,906,999, JP-A 9-301948, JP-A 2000-314956, JP-A 2001-233842, and International Publication 2004-074242.

By further subjecting the sulfonium salt, iodonium salt, imide sulfonate or oxime sulfonate described above to hydrolysis or solvolysis in a solvent mixture of water and alcohol or acetone in the presence of a base such as sodium hydroxide in a standard way, a compound having formula (2), (2a), (2b), (3a) or (3b) can be synthesized. More specifically, a compound having formula (1a) can be synthesized by subjecting 2-acyloxy-1,1,3,3,3-pentafluoro-1-sulfonic acid salt to hydrolysis in water in the presence of a base such as sodium hydroxide or tetrabutylammonium hydroxide. Formation of the compound (1a) can be confirmed by nuclear magnetic resonance with ¹⁹F (¹⁹F-NMR) and time-of-flight mass spectrometry (TOFMS). Subsequent anion exchange by a standard technique can yield a compound having formula (2), (2a) or (2b).

In preparing the sulfonate salt described above, a sulfonate salt of the following general formula (1a′) or (1a″) corresponding to the sulfonate salt of formula (1a) with hydrogen fluoride being eliminated can sometimes form as well. CF₃—C(OH)═CFSO₃ ⁻M⁺  (1a′) CF₂═C(OH)CF₂SO₃ ⁻M⁺  (1a″) Herein, M⁺ is a lithium, sodium, potassium, ammonium or tetramethylammonium ion.

When the sulfonate salt preparing method yields a mixture of such sulfonate salts, the molar ratio of the sulfonate salt of formula (1a) as the major component to the sulfonate salt of formula (1a′) or (1a″) is often in a range from 100:0 to 100:10.

It is noted for the sulfonate salt of formula (1a′) or (1a″) or homologues that on time-of-flight mass spectrometry (TOFMS), aside from the major anion, an anion having a mass number smaller by 20 than the major anion is sometimes observed on the negative side as a minute peak although a chance of observation depends on an existence ratio and sensitivity.

The sulfonate salt of formula (1a′) or (1a″) may be used alone or in admixture with the sulfonate salt of formula (1a) to synthesize a photoacid generator, sulfonium salt, iodonium salt, N-sulfonyloxyimide compound or oxime sulfonate compound. The photoacid generator synthesized using the sulfonate salt of formula (1a′) or (1a″) as the starting reactant may be included in resist compositions, especially chemically amplified positive resist compositions, or applied to a patterning process.

Specifically, still further embodiments of the invention include

a photoacid generator for chemically amplified resist compositions which generates a sulfonic acid having the general formula (1′) or (1″) upon exposure to high-energy radiation selected from UV, deep-UV, electron beam, x-ray, excimer laser, gamma-ray and synchrotron radiation, CF₃—C(OH)═CFSO₃ ⁻H⁺  (1′) CF₂═C(OH)CF₂SO₃ ⁻H⁺  (1″);

a sulfonium salt having the general formula (2′) or (2″): R¹R²R³S⁺CF₃—C(OH)═CFSO₃ ⁻  (2′) R¹R²R³S⁺CF₂═C(OH)CF₂SO₃ ⁻  (2″) wherein R¹, R² and R³ are each independently a substituted or unsubstituted, straight or branched C₁-C₁₀ alkyl, alkenyl or oxoalkyl group, or a substituted or unsubstituted C₆-C₁₈ aryl, aralkyl or aryloxoalkyl group, or any two or more of R¹, R² and R³ may bond together to form a ring with the sulfur atom;

a sulfonium salt having the general formula (2a′) or (2a″): (R⁴—(O)_(n))_(m)-PhS⁺Ph₂CF₃—C(OH)═CFSO₃ ⁻  (2a′) (R⁴—(O)_(n))_(m)-PhS⁺Ph₂CF₂═C(OH)CF₂SO₃ ⁻  (2a″) wherein R⁴ is a substituted or unsubstituted, straight, branched or cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or unsubstituted C₆-C₁₄ aryl group, Ph is phenyl, m is 1 to 5, and n is 0 or 1;

a iodonium salt having the general formula (2b′) or (2b″): R⁴(O)_(n)-PhI⁺Ph(O)_(n)—R⁴CF₃—C(OH)═CFSO₃ ⁻  (2b′) R⁴(O)_(n)-PhI⁺Ph(O)_(n)—R⁴CF₂═C(OH)CF₂SO₃ ⁻  (2b″) wherein R⁴, Ph and n are as defined above;

a N-sulfonyloxyimide compound having the general formula (3a′) or (3a″):

wherein X and Y are each independently hydrogen or a substituted or unsubstituted C₁-C₆ alkyl group, or X and Y may bond together to form a saturated or unsaturated C₆-C₁₂ ring with the carbon atoms to which they are attached, and Z is a single bond, double bond, methylene group or oxygen atom; and

an oxime sulfonate compound having the general formula (3b′) or (3b″):

wherein q is 0 or 1; p is a single bond, a substituted or unsubstituted C₁-C₂₀ alkyl group or a substituted or unsubstituted C₆-C₁₅ aryl group when q is 0; or p is a substituted or unsubstituted C₁-C₂₀ alkylene group or a substituted or unsubstituted C₆-C₁₅ arylene group when q is 1; EWG is a cyano, trifluoromethyl, perfluoroethyl, perfluoropropyl, 5H-perfluoropentyl, 6H-perfluorohexyl, nitro or methyl group, and when q is 1, two EWG's may bond together to form a ring of 6 carbon atoms with the carbon atoms to which they are attached.

The compounds of the still further embodiments serve as photoacid generators and may be included in resist compositions or applied to patterning processes in the same manner as the preceding embodiments of the invention as will be described later.

It is noted that by reacting the sulfonate salt of formula (1a) or the sulfonate of formula (2), (2a), (2b), (3a), or (3b) obtained by the above-described method with a carboxylic halide or carboxylic anhydride in a solvent such as methylene chloride or acetonitrile in the presence of a base such as triethylamine, there can be obtained a sulfonate salt or a sulfonium salt, iodonium salt, imide sulfonate or oxime sulfonate photoacid generator having a carboxylic acid ester in the molecule. By reacting the same with a difunctional carboxylic halide such as adipic chloride, there can be synthesized a difunctional sulfonate salt or a difunctional sulfonium salt, iodonium salt, imide sulfonate or oxime sulfonate photoacid generator.

As described above, a first embodiment of the present invention provides a photoacid generator for chemically amplified resist compositions which generates a sulfonic acid having formula (1) upon exposure to high-energy radiation. A second embodiment of the present invention provides a sulfonium salt, iodonium salt, dicarboxylimide sulfonate, and oxime sulfonate serving as photoacid generators in chemically amplified resist compositions. A third embodiment of the present invention provides a resist composition comprising a photoacid generator which generates a sulfonic acid having formula (1) upon exposure to high-energy radiation and a resin which changes its solubility in an alkaline developer liquid under the action of acid.

The resist composition of the invention is typically embodied as

(i) a chemically amplified positive resist composition comprising

(A) a photoacid generator which generates a sulfonic acid having formula (1) upon exposure to high-energy radiation,

(B) an organic solvent,

(C) a base resin which changes its solubility in an alkaline developer liquid under the action of acid, and

one or more optional components including (D) a basic compound, (E) a photoacid generator other than (A), (F) an organic acid derivative and/or fluorinated alcohol, and (G) a dissolution inhibitor having a molecular weight of up to 3,000; and

(ii) a chemically amplified negative resist composition comprising

(A) a photoacid generator which generates a sulfonic acid having formula (1) upon exposure to high-energy radiation,

(B) an organic solvent,

(C′) a base resin which is normally alkali soluble, but becomes substantially alkali insoluble under the action of a crosslinker,

(H) a crosslinker which induces crosslinkage under the action of acid, and

one or more optional components including (D) a basic compound and (E) a photoacid generator other than (A).

The PAG which generates a sulfonic acid having formula (1) as component (A) is as described above. More specifically, it is a compound having formula (2), (2a), (2b), (3a) or (3b). In the resist composition, the PAG is compounded in an amount of 0.1 to 10 parts, more preferably 1 to 7 parts by weight per 100 parts by weight of the base resin.

Component B

The organic solvent used herein may be any organic solvent in which the base resin, photoacid generator, and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl amyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; and lactones such as γ-butyrolactone. These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, it is recommended to use diethylene glycol dimethyl ether, 1-ethoxy-2-propanol, propylene glycol monomethyl ether acetate (PGMEA), cyclohexanone and mixtures thereof because the photoacid generator is most soluble therein.

An appropriate amount of the organic solvent used is about 200 to 3,000 parts, especially about 400 to 2,000 parts by weight per 100 parts by weight of the base resin.

Component C

The base resins used as component (C) or (C′) in the inventive compositions include polyhydroxystyrene (PHS), and copolymers of PHS with styrene, (meth)acrylic acid esters or other polymerizable olefinic compounds, for KrF excimer laser resist use; (meth)acrylic acid ester polymers, alternating copolymers of cycloolefin with maleic anhydride, copolymers further containing vinyl ethers or (meth)acrylic acid esters, polynorbornene, ring-opening metathesis polymerized cycloolefins, and hydrogenated ring-opening metathesis polymerized cycloolefins, for ArF excimer laser resist use; and fluorinated forms of the foregoing polymers (for both KrF and ArF laser uses) for F₂ excimer laser resist use, although the base resins are not limited to these polymers.

Understandably, the sulfonium salts and iodonium salts having polymerizable substituent groups according to the invention may be used as a monomer component in forming the base resin. Typical sulfonium and iodonium salts for such use are combinations of onium cations such as (4-acryloyloxyphenyl)diphenylsulfonium, (4-methacryloyloxyphenyl)diphenylsulfonium, (4-acryloyloxyphenyl)phenyliodonium, and (4-methacryloyloxyphenyl)phenyliodonium cations with anions such as 1,1,3,3,3-pentafluoro-2-hydroxypropane-1-sulfonate.

The base resins may be used alone or in admixture of two or more. In the case of positive resist compositions, it is a common practice to substitute acid labile groups for hydroxyl groups on phenol, carboxyl groups or fluorinated alkyl alcohols for reducing the rate of dissolution in unexposed regions.

The base resins are not limited to the foregoing resins. Use may also be made of the resins described in the following patents.

JP-A 2000-159758 JP-A 2000-186118 JP-A 2000-309611 JP-A 2000-327633 JP-A 2000-330283 JP-A 2001-329052 JP-A 2002-202609 JP-A 2002-161116 JP-A 2003-2883 JP-A 2003-20313 JP-A 2003-26728 JP-A 2003-34706 JP-A 2003-64134 JP-A 2003-66612 JP-A 2003-113213 JP-A 2003-316027 JP-A 2003-321466 JP-A 2004-143153 JP-A 2004-124082 JP-A 2004-115486 JP-A 2004-62175

In a preferred embodiment, the base resin is at least one polymer selected from among poly(meth)acrylic acid and derivatives thereof, alternating copolymers of a cycloolefin derivative and maleic anhydride, copolymers of three or more components comprising a cycloolefin derivative, maleic anhydride, and polyacrylic acid or derivatives thereof, cycloolefin derivative-α-trifluoromethyl acrylate copolymers, polynorbornene, ring-opening metathesis polymers, and hydrogenated ring-opening metathesis polymers.

In another preferred embodiment, the base resin is a polymeric structure containing silicon atoms or a polymeric structure containing fluorine atoms. Such polymers include those described in the following patents.

JP-A 2005-8765 JP-A 2004-354417 JP-A 2004-352743 JP-A 2004-331854 JP-A 2004-331853 JP-A 2004-292781 JP-A 2004-252405 JP-A 2004-190036 JP-A 2004-115762 JP-A 2004-83873 JP-A 2004-59844 JP-A 2004-35671 JP-A 2004-83900 JP-A 2004-99689 JP-A 2004-145048 JP-A 2004-217533 JP-A 2004-231815 JP-A 2004-244439 JP-A 2004-256562 JP-A 2004-307447 JP-A 2004-323422 JP-A 2005-29527 JP-A 2005-29539

Included in the chemically amplified positive resist composition is a base resin having acid labile groups which is normally insoluble or substantially insoluble in developer, but becomes soluble in developer as a result of the acid labile groups being eliminated under the action of acid.

The acid labile groups to be introduced into the base resin may be selected from a variety of such groups, preferably from C₂-C₃₀ acetal groups and tertiary C₄-C₃₀ alkyl groups having the formulae (C1) and (C2), respectively.

In formulae (C1) and (C2), R⁵ and R⁶ each are hydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group, which may contain a hetero atom such as oxygen, sulfur, nitrogen or fluorine, R⁷, R⁸, R⁹ and R¹⁰ each are a straight, branched or cyclic C₁-C₂₀ alkyl group, a C₆-C₁₀ aryl group or a C₇-C₁₀ aralkyl group, which may contain a hetero atom such as oxygen, sulfur, nitrogen or fluorine. A pair of R⁵ and R⁶, a pair of R⁵ and R⁷, a pair of R⁶ and R⁷, a pair of R⁸ and R⁹, a pair of R⁸ and R¹⁰, or a pair of R⁹ and R¹⁰, taken together, may form a ring of 3 to 30 carbon atoms with the carbon atom to which they are attached.

Illustrative examples of the acetal group of formula (C1) include, but are not limited to, methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, isopropoxymethyl, t-butoxymethyl, 1-methoxyethyl, 1-methoxypropyl, 1-methoxybutyl, 1-ethoxyethyl, 1-ethoxypropyl, 1-ethoxybutyl, 1-propoxyethyl, 1-propoxypropyl, 1-propoxybutyl, 1-cyclopentyloxyethyl, 1-cyclohexyloxyethyl, 2-methoxyisopropyl, 2-ethoxyisopropyl, 1-phenoxyethyl, 1-benzyloxyethyl, 1-phenoxypropyl, 1-benzyloxypropyl, 1-adamantyloxyethyl, 1-adamantyloxypropyl, 2-tetrahydrofuryl, 2-tetrahydro-2H-pyranyl, 1-(2-cyclohexanecarbonyloxyethoxy)ethyl, 1-(2-cyclohexanecarbonyloxyethoxy)propyl, 1-[2-(1-adamantylcarbonyloxy)ethoxy]ethyl, and 1-[2-(1-adamantylcarbonyloxy)ethoxy]propyl.

Illustrative examples of the tertiary alkyl group of formula (C2) include, but are not limited to, t-butyl, t-pentyl, 1-ethyl-1-methylpropyl, 1,1-diethylpropyl, 1,1,2-trimethylpropyl, 1-adamantyl-1-methylethyl, 1-methyl-1-(2-norbornyl)ethyl, 1-methyl-1-(tetrahydrofuran-2-yl)ethyl, 1-methyl-1-(7-oxanorbornan-2-yl)ethyl, 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-propylcyclopentyl, 1-cyclopentylcyclopentyl, 1-cyclohexylcyclopentyl, 1-(2-tetrahydrofuryl)cyclopentyl, 1-(7-oxanorbornan-2-yl)cyclopentyl, 1-methylcyclohexyl, 1-ethylcyclohexyl, 1-cyclopentylcyclohexyl, 1-cyclohexylcyclohexyl, 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 8-methyl-8-tricyclo[5.2.1.0^(2,6)]decyl, 8-ethyl-8-tricyclo[5.2.1.0.^(2,6)]decyl, 3-methyl-3-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl, 3-ethyl-3-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1-methyl-3-oxo-1-cyclohexyl, 1-methyl-1-(tetrahydrofuran-2-yl)ethyl, 5-hydroxy-2-methyl-2-adamantyl, and 5-hydroxy-2-ethyl-2-adamantyl.

In the base resin, at least 1 mol % of hydrogen atoms of hydroxyl groups may be substituted by acid labile groups of the following general formula (C3a) or (C3b) for crosslinkage between molecules or within a molecule.

Herein, R¹¹ and R¹² each are hydrogen or a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, or R¹¹ and R¹², taken together, may form a ring, with the proviso that each of R¹¹ and R¹² is a straight or branched alkylene group of 1 to 8 carbon atoms when they form a ring. R¹³ is a straight, branched or cyclic. alkylene group of 1 to 10 carbon atoms. Letter “a” is an integer of 1 to 7 and “b” is 0 or an integer of 1 to 10. “A” is a (a+1)-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbon atoms, which may have an intervening hetero atom and in which the hydrogen atom attached to a carbon atom may be partially replaced by a hydroxyl group, carboxyl group, carbonyl group or fluorine atom. B is —CO—O—, —NHCO—O— or —NHCONH—.

Illustrative examples of the crosslinking acetal linkages represented by formulae (C3a) and (C3b) are given below as (C3)-1 through (C3)-8, but not limited thereto.

Preferably the base resin has a weight average molecular weight (Mw) of 2,000 to 100,000, as measured by gel permeation chromatography (GPC) versus polystyrene standards. With Mw below 2,000, film formation and resolution may become poor. With Mw beyond 100,000, resolution may become poor or foreign matter may generate during pattern formation.

In the base resin, the proportion of acid labile group-containing monomer units relative to the other monomer units (constituent units) is typically in a range of 10 to 70%, preferably 20 to 60%, in case intended for ArF excimer laser resist compositions; and typically in a range of 10 to 50%, preferably 20 to 40%, in case intended for KrF excimer laser resist compositions.

The monomer units other than the acid labile group-containing monomer units are preferably monomer units containing polar groups such as alcohols, fluorinated alcohols, and ether, lactone, ester, acid anhydride, and carboxylic acid in the case of the base resins for ArF excimer laser resist compositions. The base resins for KrF excimer laser resist compositions may comprise units of styrene, indene and 4-acetoxystyrene in addition to 4-hydroxystyrene units having no acid labile groups incorporated. The monomer units may be of one type or of two or more different types.

Component D

The basic compound used as component (D) is preferably a compound capable of suppressing the rate of diffusion when the acid generated by the photoacid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure and reduces substrate and environment dependence, as well as improving the exposure latitude and the pattern profile.

Examples of basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, nitrogen-containing compounds with carboxyl group, nitrogen-containing compounds with sulfonyl group, nitrogen-containing compounds with hydroxyl group, nitrogen-containing compounds with hydroxyphenyl group, alcoholic nitrogen-containing compounds, amide derivatives, and imide derivatives.

Examples of suitable primary aliphatic amines include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylenepentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, triisobutylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,N′,N′-tetramethylmethylenediamine, N,N,N′,N′-tetramethylethylenediamine, and N,N,N′,N′-tetramethyltetraethylenepentamine.

Examples of suitable mixed amines include dimethylethylamine, methylethylpropylamine, benzylamine, phenethylamine, and benzyldimethylamine. Examples of suitable aromatic and heterocyclic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene, pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridone, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.

Examples of suitable nitrogen-containing compounds with carboxyl group include aminobenzoic acid, indolecarboxylic acid, and amino acid derivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples of suitable nitrogen-containing compounds with sulfonyl group include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples of suitable nitrogen-containing compounds with hydroxyl group, nitrogen-containing compounds with hydroxyphenyl group, and alcoholic nitrogen-containing compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine, triisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]piperazine, piperidine ethanol, 1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide. Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable imide derivatives include phthalimide, succinimide, and maleimide.

In addition, basic compounds of the following general formula (Am)-1 may also be included alone or in admixture. N(Rx)_(k)(Ry)_(3−k)  (Am)-1

In the formula, k is equal to 1, 2 or 3; the side chain Ry is independently hydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group which may contain a hydroxyl or ether group; and the side chain Rx is independently selected from groups of the following general formulas (Rx)-1 to (Rx)-3, and two or three Rx may bond together to form a ring.

In the formulas, R³⁰¹, R³⁰³ and R³⁰⁶ are independently straight or branched C₁-C₄ alkylene groups; R³⁰² and R³⁰⁵ are independently hydrogen or straight, branched or cyclic C₁-C₂₀ alkyl groups, which may contain at least one hydroxyl group, ether group, ester group or lactone ring; R³⁰⁴ is a single bond or a straight or branched C₁-C₄ alkylene group; R³⁰⁷ is a straight, branched or cyclic C₁-C₂₀ alkyl group, which may contain at least one hydroxyl group, ether group, ester group or lactone ring.

Illustrative examples of the basic compounds of formula (Am)-1 include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4, 1-aza-15-crown-5, 1-aza-18-crown-6, tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine, tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine, tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)amine, tris(2-pivaloyloxyethyl)amine, N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine, tris(2-methoxycarbonyloxyethyl)amine, tris(2-tert-butoxycarbonyloxyethyl)amine, tris[2-(2-oxopropoxy)ethyl]amine, tris[2-(methoxycarbonylmethyl)oxyethyl]amine, tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine, tris[2-(cyclohexyloxycarbonylmethyloxy)ethyl]amine, tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine, N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]-ethylamine, N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]-ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)-ethylamine, N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)-ethylamine, N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxy-carbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxy-carbonyl]ethylamine, N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)-ethylamine, N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)-ethylamine, N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)ethylamine, N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine, N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine, N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine, N-methyl-bis(2-pivaloyloxyethyl)amine, N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine, N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]amine, tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine, N-butyl-bis(methoxycarbonylmethyl)amine, N-hexyl-bis(methoxycarbonylmethyl)amine, and β-(diethylamino)-δ-valerolactone.

Also useful are one or more of cyclic structure-bearing basic compounds having the following general formula (Am)-2.

Herein Rx is as defined above, and R³⁰⁸ is a straight or branched C₂-C₂₀ alkylene group which may contain one or more carbonyl, ether, ester or sulfide groups.

Illustrative examples of the cyclic structure-bearing basic compounds having formula (Am)-2 include 1-[2-(methoxymethoxy)ethyl]pyrrolidine, 1-[2-(methoxymethoxy)ethyl]piperidine, 4-[2-(methoxymethoxy)ethyl]morpholine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]pyrrolidine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]piperidine, 4-[2-[(2-methoxyethoxy)methoxy]ethyl]morpholine, 2-(1-pyrrolidinyl)ethyl acetate, 2-piperidinoethyl acetate, 2-morpholinoethyl acetate, 2-(1-pyrrolidinyl)ethyl formate, 2-piperidinoethyl propionate, 2-morpholinoethyl acetoxyacetate, 2-(1-pyrrolidinyl)ethyl methoxyacetate, 4-[2-(methoxycarbonyloxy)ethyl]morpholine, 1-[2-(t-butoxycarbonyloxy)ethyl]piperidine, 4-[2-(2-methoxyethoxycarbonyloxy)ethyl]morpholine, methyl 3-(1-pyrrolidinyl)propionate, methyl 3-piperidinopropionate, methyl 3-morpholinopropionate, methyl 3-(thiomorpholino)propionate, methyl 2-methyl-3-(1-pyrrolidinyl)propionate, ethyl 3-morpholinopropionate, methoxycarbonylmethyl 3-piperidinopropionate, 2-hydroxyethyl 3-(1-pyrrolidinyl)propionate, 2-acetoxyethyl 3-morpholinopropionate, 2-oxotetrahydrofuran-3-yl 3-(1-pyrrolidinyl)propionate, tetrahydrofurfuryl 3-morpholinopropionate, glycidyl 3-piperidinopropionate, 2-methoxyethyl 3-morpholinopropionate, 2-(2-methoxyethoxy)ethyl 3-(1-pyrrolidinyl)propionate, butyl 3-morpholinopropionate, cyclohexyl 3-piperidinopropionate, α-(1-pyrrolidinyl)methyl-γ-butyrolactone, β-piperidino-γ-butyrolactone, β-morpholino-δ-valerolactone, methyl 1-pyrrolidinylacetate, methyl piperidinoacetate, methyl morpholinoacetate, methyl thiomorpholinoacetate, ethyl 1-pyrrolidinylacetate, and 2-methoxyethyl morpholinoacetate.

Also, one or more of cyano-bearing basic compounds having the following general formulae (Am)-3 to (Am)-6 may be blended.

Herein, Rx, R³⁰⁸ and k are as defined above, and R³⁰⁹ and R³¹⁰ each are independently a straight or branched C₁-C₄ alkylene group.

Illustrative examples of the cyano-bearing basic compounds having formulae (Am)-3 to (Am)-6 include 3-(diethylamino)propiononitrile, N,N-bis(2-hydroxyethyl)-3-aminopropiononitrile, N,N-bis(2-acetoxyethyl)-3-aminopropiononitrile, N,N-bis(2-formyloxyethyl)-3-aminopropiononitrile, N,N-bis(2-methoxyethyl)-3-aminopropiononitrile, N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, methyl N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropionate, methyl N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropionate, N-(2-cyanoethyl)-N-ethyl-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropiononitrile, N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-formyloxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-[2-(methoxymethoxy)ethyl]-3-aminopropiono-nitrile, N-(2-cyanoethyl)-N-(3-hydroxy-1-propyl)-3-aminopropiono-nitrile, N-(3-acetoxy-1-propyl)-N-(2-cyanoethyl)-3-aminopropiono-nitrile, N-(2-cyanoethyl)-N-(3-formyloxy-1-propyl)-3-aminopropiono-nitrile, N-(2-cyanoethyl)-N-tetrahydrofurfuryl-3-aminopropiononitrile, N,N-bis(2-cyanoethyl)-3-aminopropiononitrile, diethylaminoacetonitrile, N,N-bis(2-hydroxyethyl)aminoacetonitrile, N,N-bis(2-acetoxyethyl)aminoacetonitrile, N,N-bis(2-formyloxyethyl)aminoacetonitrile, N,N-bis(2-methoxyethyl)aminoacetonitrile, N,N-bis[2-(methoxymethoxy)ethyl]aminoacetonitrile, methyl N-cyanomethyl-N-(2-methoxyethyl)-3-aminopropionate, methyl N-cyanomethyl-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-cyanomethyl-3-aminopropionate, N-cyanomethyl-N-(2-hydroxyethyl)aminoacetonitrile, N-(2-acetoxyethyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(2-formyloxyethyl)aminoacetonitrile, N-cyanomethyl-N-(2-methoxyethyl)aminoacetonitrile, N-cyanomethyl-N-[2-(methoxymethoxy)ethyl)aminoacetonitrile, N-cyanomethyl-N-(3-hydroxy-1-propyl)aminoacetonitrile, N-(3-acetoxy-1-propyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(3-formyloxy-1-propyl)aminoacetonitrile, N,N-bis(cyanomethyl)aminoacetonitrile, 1-pyrrolidinepropiononitrile, 1-piperidinepropiononitrile, 4-morpholinepropiononitrile, 1-pyrrolidineacetonitrile, 1-piperidineacetonitrile, 4-morpholineacetonitrile, cyanomethyl 3-diethylaminopropionate, cyanomethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, 2-cyanoethyl 3-diethylaminopropionate, 2-cyanoethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-amino-propionate, cyanomethyl 1-pyrrolidinepropionate, cyanomethyl 1-piperidinepropionate, cyanomethyl 4-morpholinepropionate, 2-cyanoethyl 1-pyrrolidinepropionate, 2-cyanoethyl 1-piperidinepropionate, and 2-cyanoethyl 4-morpholinepropionate.

Also included are basic compounds as described in JP-A 2004-347736 and JP-A 2004-347738.

The basic compounds may be used alone or in admixture of two or more. The basic compound is preferably formulated in an amount of 0 to 2 parts, and especially 0.05 to 1 part by weight, per 100 parts by weight of the base resin.

Component E

In one preferred embodiment, the resist composition further contains (E) a compound capable of generating an acid upon exposure to high-energy radiation (e.g., UV. deep UV, electron beam, x-ray, excimer laser beam, gamma-ray or synchrotron radiation), that is, an auxiliary photoacid generator other than component (A). Suitable auxiliary photoacid generators include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxydicarboxyimide, O-arylsulfonyloxime and O-alkylsulfonyloxime photoacid generators. Exemplary auxiliary photoacid generators are given below while they may be used alone or in admixture of two or more.

Sulfonium salts are salts of sulfonium cations with sulfonates, bis(substituted alkylsulfonyl)imides and tris(substituted alkylsulfonyl)methides. Exemplary sulfonium cations include triphenylsulfonium, (4-tert-butoxyphenyl)diphenylsulfonium, bis(4-tert-butoxyphenyl)phenylsulfonium, tris(4-tert-butoxyphenyl)sulfonium, (3-tert-butoxyphenyl)diphenylsulfonium, bis(3-tert-butoxyphenyl)phenylsulfonium, tris(3-tert-butoxyphenyl)sulfonium, (3,4-di-tert-butoxyphenyl)diphenylsulfonium, bis(3,4-di-tert-butoxyphenyl)phenylsulfonium, tris(3,4-di-tert-butoxyphenyl)sulfonium, diphenyl(4-thiophenoxyphenyl)sulfonium, (4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium, tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium, (4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium, tris(4-dimethylaminophenyl)sulfonium, 4-methylphenyldiphenylsulfonium, 4-tert-butylphenyldiphenylsulfonium, bis(4-methylphenyl)phenylsulfonium, bis(4-tert-butylphenyl)phenylsulfonium, tris(4-methylphenyl)sulfonium, tris(4-tert-butylphenyl)sulfonium, tris(phenylmethyl)sulfonium, 2-naphthyldiphenylsulfonium, dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium, 4-methoxyphenyldimethylsulfonium, trimethylsulfonium, 2-oxocyclohexylcyclohexylmethylsulfonium, trinaphthylsulfonium, tribenzylsulfonium, diphenylmethylsulfonium, dimethylphenylsulfonium, 2-oxopropylthiacyclopentanium, 2-oxobutylthiacyclopentanium, 2-oxo-3,3-dimethylbutylthiacyclopentanium, 2-oxo-2-phenylethylthiacyclopentanium, 4-n-butoxynaphthyl-1-thiacyclopentanium, and 2-n-butoxynaphthyl-1-thiacyclopentanium.

-   Exemplary sulfonates include trifluoromethanesulfonate,     pentafluoroethanesulfonate, heptafluoropropanesulfonate,     nonafluorobutanesulfonate, tridecafluorohexanesulfonate,     heptadecafluorooctanesulfonate,     perfluoro-4-ethylcyclohexanesulfonate,     2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,     4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,     mesitylenesulfonate, 2,4,6-triisopropylbenzenesulfonate,     toluenesulfonate, benzenesulfonate,     4-(4′-toluenesulfonyloxy)benzenesulfonate,     6-(4-toluenesulfonyloxy)naphthalene-2-sulfonate,     4-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     5-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     8-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     naphthalenesulfonate, camphorsulfonate, octanesulfonate,     dodecylbenzenesulfonate, butanesulfonate, methanesulfonate,     1,1-difluoro-2-naphthyl-ethanesulfonate,     1,1,2,2-tetrafluoro-2-(norbornan-2-yl)ethanesulfonate, and     1,1,2,2-tetrafluoro-2-(tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-en-8-yl)ethanesulfonate. -   Exemplary bis(substituted alkylsulfonyl)imides include     bistrifluoromethylsulfonylimide, bispentafluoroethylsulfonylimide,     bisheptafluoropropylsulfonylimide, and     1,3-propylenebissulfonylimide. A typical tris(substituted     alkylsulfonyl)methide is tristrifluoromethylsulfonylmethide.     Sulfonium salts based on combination of the foregoing examples are     included.

Iodonium salts are salts of iodonium cations with sulfonates, bis(substituted alkylsulfonyl)imides and tris(substituted alkylsulfonyl)methides.

-   Exemplary iodonium cations are aryliodonium cations including     diphenyliodinium, bis(4-tert-butylphenyl)iodonium,     4-tert-butoxyphenylphenyliodonium, and     4-methoxyphenylphenyliodonium. Exemplary sulfonates include     trifluoromethanesulfonate, pentafluoroethanesulfonate,     heptafluoropropanesulfonate, nonafluorobutanesulfonate,     tridecafluorohexanesulfonate, heptadecafluorooctanesulfonate,     perfluoro-4-ethylcyclohexanesulfonate,     2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,     4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,     mesitylenesulfonate, 2,4,6-triisopropylbenzenesulfonate,     toluenesulfonate, benzenesulfonate,     4-(4′-toluenesulfonyloxy)benzenesulfonate,     6-(4-toluenesulfonyloxy)naphthalene-2-sulfonate,     4-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     5-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     8-(4-toluenesulfonyloxy)naphthalene-1-sulfonate,     naphthalenesulfonate, camphorsulfonate, octanesulfonate,     dodecylbenzenesulfonate, butanesulfonate, methanesulfonate,     1,1-difluoro-2-naphthyl-ethanesulfonate,     1,1,2,2-tetrafluoro-2-(norbornan-2-yl)ethanesulfonate, and     1,1,2,2-tetrafluoro-2-(tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-en-8-yl)ethanesulfonate. -   Exemplary bis(substituted alkylsulfonyl)imides include     bistrifluoromethylsulfonylimide, bispentafluoroethylsulfonylimide,     bisheptafluoropropylsulfonylimide, and     1,3-propylenebissulfonylimide. A typical tris(substituted     alkylsulfonyl)methide is tristrifluoromethylsulfonylmethide.     Iodonium salts based on combination of the foregoing examples are     included.

Exemplary sulfonyldiazomethane compounds include bissulfonyldiazomethane compounds and sulfonyl-carbonyldiazomethane compounds such as bis(ethylsulfonyl)diazomethane, bis(1-methylpropylsulfonyl)diazomethane, bis(2-methylpropylsulfonyl)diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(perfluoroisopropylsulfonyl)diazomethane, bis(phenylsulfonyl)diazomethane, bis(4-methylphenylsulfonyl)diazomethane, bis(2,4-dimethylphenylsulfonyl)diazomethane, bis(4-acetyloxyphenylsulfonyl)diazomethane, bis(4-methanesulfonyloxyphenylsulfonyl)diazomethane, bis(4-(4-toluenesulfonyloxy)phenylsulfonyl)diazomethane, bis(2-naphthylsulfonyl)diazomethane, 4-methylphenylsulfonylbenzoyldiazomethane, tert-butylcarbonyl-4-methylphenylsulfonyldiazomethane, 2-naphthylsulfonylbenzoyldiazomethane, 4-methylphenylsulfonyl-2-naphthoyldiazomethane, methylsulfonylbenzoyldiazomethane, and tert-butoxycarbonyl-4-methylphenylsulfonyldiazomethane.

N-sulfonyloxydicarboxyimide photoacid generators include combinations of imide skeletons with sulfonates.

-   Exemplary imide skeletons are succinimide,     naphthalenedicarboxyimide, phthalimide, cyclohexyldicarboxyimide,     5-norbornene-2,3-dicarboxyimide, and     7-oxabicyclo[2.2.1]-5-heptene-2,3-dicarboxyimide. -   Exemplary sulfonates include trifluoromethanesulfonate,     pentafluoroethanesulfonate, heptafluoropropanesulfonate,     nonafluorobutanesulfonate, tridecafluorohexanesulfonate,     heptadecafluorooctanesulfonate,     perfluoro-4-ethylcyclohexanesulfonate,     2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,     4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,     mesitylenesulfonate, 2,4,6-triisopropylbenzenesulfonate,     toluenesulfonate, benzenesulfonate, naphthalenesulfonate,     camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,     butanesulfonate, methanesulfonate,     1,1-difluoro-2-naphthyl-ethanesulfonate,     1,1,2,2-tetrafluoro-2-(norbornan-2-yl)ethanesulfonate, and     1,1,2,2-tetrafluoro-2-(tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-en-8-yl)ethanesulfonate.

Benzoinsulfonate photoacid generators include benzoin tosylate, benzoin mesylate, and benzoin butanesulfonate.

Pyrogallol trisulfonate photoacid generators include pyrogallol, fluoroglycine, catechol, resorcinol, hydroquinone, in which all the hydroxyl groups are substituted by trifluoromethanesulfonate, pentafluoroethanesulfonate, heptafluoropropanesulfonate, nonafluorobutanesulfonate, tridecafluorohexanesulfonate, heptadecafluorooctanesulfonate, perfluoro-4-ethylcyclohexanesulfonate, 2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate, naphthalenesulfonate, camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate, butanesulfonate, methanesulfonate, 1,1-difluoro-2-naphthyl-ethanesulfonate, 1,1,2,2-tetrafluoro-2-(norbornan-2-yl)ethanesulfonate, 1,1,2,2-tetrafluoro-2-(tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-en-8-yl)ethanesulfonate or the like.

Nitrobenzyl sulfonate photoacid generators include 2,4-dinitrobenzyl sulfonate, 2-nitrobenzyl sulfonate, and 2,6-dinitrobenzyl sulfonate, with exemplary sulfonates including trifluoromethanesulfonate, pentafluoroethanesulfonate, heptafluoropropanesulfonate, nonafluorobutanesulfonate, tridecafluorohexanesulfonate, heptadecafluorooctanesulfonate, perfluoro-4-ethylcyclohexanesulfonate, 2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate, naphthalenesulfonate, camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate, butanesulfonate, methanesulfonate, 1,1-difluoro-2-naphthyl-ethanesulfonate, 1,1,2,2-tetrafluoro-2-(norbornan-2-yl)ethanesulfonate, 1,1,2,2-tetrafluoro-2-(tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-en-8-yl)ethanesulfonate. Also useful are analogous nitrobenzyl sulfonate compounds in which the nitro group on the benzyl side is substituted by a trifluoromethyl group.

Sulfone photoacid generators include bis(phenylsulfonyl)methane, bis(4-methylphenylsulfonyl)methane, bis(2-naphthylsulfonyl)methane, 2,2-bis(phenylsulfonyl)propane, 2,2-bis(4-methylphenylsulfonyl)propane, 2,2-bis(2-naphthylsulfonyl)propane, 2-methyl-2-(p-toluenesulfonyl)propiophenone, 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane, and 2,4-dimethyl-2-(p-toluenesulfonyl)pentan-3-one.

Suitable O-arylsulfonyloxime compounds and O-alkylsulfonyloxime compounds (oxime sulfonates) include photoacid generators in the form of glyoxime derivatives (as described in Japanese Patent No. 2,906,999 and JP-A 9-301948); photoacid generators in the form of oxime sulfonates with a long conjugated system separated by thiophene or cyclohexadiene (as described in U.S. Pat. No. 6,004,724); oxime sulfonates having an electron withdrawing group such as trifluoromethyl incorporated for increased stability (as described in U.S. Pat. No. 6,261,738, JP-A 2000-314956, International Publication No. 2004-074242); oxime sulfonates using phenylacetonitrile or substituted acetonitrile derivatives (as described in JP-A 9-95479, JP-A 9-230588 and the compounds described in the prior art section thereof); and bisoxime sulfonates (as described in JP-A 9-208554, GB 2348644A, JP-A 2002-278053).

When the photoacid generator (E) is added to the KrF excimer laser resist composition, preference is given to sulfonium salts, bissulfonyldiazomethanes, N-sulfonyloxydicarboxyimides and oxime sulfonates. Illustrative preferred photoacid generators include triphenylsulfonium p-toluenesulfonate, triphenylsulfonium camphorsulfonate, triphenylsulfonium pentafluorobenzenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium 4-(p-toluenesulfonyloxy)benzenesulfonate, triphenylsulfonium 2,4,6-triisopropylbenzenesulfonate, 4-tert-butoxyphenyldiphenylsulfonium p-toluenesulfonate, 4-tert-butoxyphenyldiphenylsulfonium camphorsulfonate, 4-tert-butoxyphenyldiphenylsulfonium 4-(p-toluenesulfonyl-oxy)benzenesulfonate, tris(4-methylphenyl)sulfonium camphorsulfonate, tris(4-tert-butylphenyl)sulfonium camphorsulfonate, bis(tert-butylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(2,4-dimethylphenylsulfonyl)diazomethane, bis(4-tert-butylphenylsulfonyl)diazomethane, N-camphorsulfonyloxy-5-norbornene-2,3-carboxylic acid imide, N-p-toluenesulfonyloxy-5-norbornene-2,3-carboxylic acid imide, (5-(10-camphorsulfonyl)oxyimino-5H-thiophen-2-ylidene)(2-methylphenyl)acetonitrile, and (5-(4-toluenesulfonyl)oxyimino-5H-thiophen-2-ylidene)(2-methylphenyl)acetonitrile.

When the photoacid generator (E) is added to the ArF laser resist composition, preference is given to sulfonium salts and oxime sulfonates. Illustrative preferred photoacid generators include triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium nonafluorobutanesulfonate, diphenyl-4-methylphenylsulfonium nonafluorobutanesulfonate, 2-oxo-2-phenylethylthiacyclopentanium nonafluorobutane-sulfonate, triphenylsulfonium perfluoro-4-ethylcyclohexanesulfonate, 4-tert-butylphenyldiphenylsulfonium nonafluorobutane-sulfonate, 4-tert-butylphenyldiphenylsulfonium heptadecafluorooctane-sulfonate, and 2,2,3,3,4,4,5,5,6,6,7,7-decafluoro-1-(2-fluorenyl)heptanone-oxime nonafluorobutanesulfonate.

When the photoacid generator (E) is added to the ArF immersion lithography resist composition, preference is given to sulfonium salts and oxime sulfonates. Illustrative preferred photoacid generators include triphenylsulfonium nonafluorobutanesulfonate, diphenyl-4-methylphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium perfluoro-4-ethylcyclohexanesulfonate, 4-tert-butylphenyldiphenylsulfonium nonafluorobutanesulfonate, 4-tert-butylphenyldiphenylsulfonium heptadecafluorooctane-sulfonate, and 2,2,3,3,4,4,5,5,6,6,7,7-decafluoro-1-(2-fluorenyl)heptanone-oxime nonafluorobutanesulfonate.

In the chemically amplified resist composition, the auxiliary photoacid generator (E) may be added in any desired amount as long as the objects of the invention are not compromised. An appropriate amount of the auxiliary photoacid generator (E) is 0 to 10 parts, and especially 0 to 5 parts by weight per 100 parts by weight of the base resin in the composition. Too high a proportion of the auxiliary photoacid generator (E) may give rise to problems of degraded resolution and foreign matter upon development and resist film peeling. The auxiliary photoacid generators may be used alone or in admixture of two or more. The transmittance of the resist film can be controlled by using an (auxiliary) photoacid generator having a low transmittance at the exposure wavelength and adjusting the amount of the photoacid generator added.

In the chemically amplified resist composition of the invention, there may be added a compound which is decomposed with an acid to generate another acid, that is, acid amplifier compound. For these compounds, reference should be made to J. Photopolym. Sci. and Tech., 8, 43-44, 45-46 (1995), and ibid., 9, 29-30 (1996).

Examples of the acid amplifier compound include tert-butyl-2-methyl-2-tosyloxymethyl acetoacetate and 2-phenyl-2-(2-tosyloxyethyl)-1,3-dioxolane, but are not limited thereto. Of well-known photoacid generators, many of those compounds having poor stability, especially poor thermal stability exhibit an acid amplifier-like behavior.

In the resist composition of the invention, an appropriate amount of the acid amplifier compound is up to 2 parts, and especially up to 1 part by weight per 100 parts by weight of the base resin. Excessive amounts of the acid amplifier compound make diffusion control difficult, leading to degradation of resolution and pattern profile.

Component F

Component (F) is an organic acid derivative and/or a fluorinated alcohol. Illustrative, non-limiting, examples of the organic acid derivatives include phenol, cresol, catechol, resorcinol, pyrogallol, fluoroglycin, bis(4-hydroxyphenyl)methane, 2,2-bis(4′-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, 1,1,1-tris(4′-hydroxyphenyl)ethane, 1,1,2-tris(4′-hydroxyphenyl)ethane, hydroxybenzophenone, 4-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, 2-hydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid, 3-(2-hydroxyphenyl)propionic acid, 2,5-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 1,2-phenylenediacetic acid, 1,3-phenylenediacetic acid, 1,4-phenylenediacetic acid, 1,2-phenylenedioxydiacetic acid, 1,4-phenylenedipropanoic acid, benzoic acid, salicylic acid, 4,4-bis(4′-hydroxyphenyl)valeric acid, 4-tert-butoxyphenylacetic acid, 4-(4-hydroxyphenyl)butyric acid, 3,4-dihydroxymandelic acid, and 4-hydroxymandelic acid. Of these, salicylic acid and 4,4-bis(4′-hydroxyphenyl)valeric acid are preferred. They may be used alone or in admixture of two or more.

The fluorinated alcohol is an alcohol which is substituted with fluorine atoms except α-position. Those compounds terminated with 1,1,1,3,3,3-hexafluoro-2-propanol are desirable although the fluorinated alcohols are not limited thereto. Illustrative examples of the desirable fluorinated alcohols are given below.

Note that R′ is selected from C₂-C₃₀ acetal groups and C₄-C₃₀ tertiaryl alkyl groups having formulae (C1) and (C2) which have been described in the “base resin” section.

In the chemically amplified resist composition of the invention, the organic acid derivative or fluorinated alcohol is preferably formulated in an amount of up to 5 parts, and especially up to 1 part by weight, per 100 parts by weight of the base resin. More than 5 parts may result in too low a resolution. Depending on the combination of the other components in the resist composition, the organic acid derivative and fluorinated alcohol may be omitted.

Component G

In one preferred embodiment, the resist composition further contains (G) a compound with a weight average molecular weight of up to 3,000 which changes its solubility in an alkaline developer under the action of an acid, that is, a dissolution inhibitor. Typically, a compound obtained by substituting acid labile substituents for some or all hydrogen atoms of hydroxyl groups on a phenol or carboxylic acid derivative having a low molecular weight of up to 2,500 or fluorinated alcohol is added as the dissolution inhibitor.

Examples of the phenol or carboxylic acid derivative having a weight average molecular weight of up to 2,500 include bisphenol A, bisphenol H, bisphenol S, 4,4-bis(4′-hydroxyphenyl)valeric acid, tris(4-hydroxyphenyl )methane, 1,1,1-tris(4′-hydroxyphenyl)ethane, 1,1,2-tris(4′-hydroxyphenyl)ethane, phenolphthalein, thymolphthalein, cholic acid, deoxycholic acid, and lithocholic acid. Examples of the fluorinated alcohol are as described above for component (F). The acid labile substituents are the same as those exemplified as the acid labile groups in the polymer.

Illustrative, non-limiting, examples of the dissolution inhibitors which are useful herein include bis(4-(2′- tetrahydropyranyloxy)phenyl)methane, bis(4-(2′-tetrahydrofuranyloxy)phenyl)methane, bis(4-tert-butoxyphenyl)methane, bis(4-tert-butoxycarbonyloxyphenyl)methane, bis(4-tert-butoxycarbonylmethyloxyphenyl)methane, bis(4-(1′-ethoxyethoxy)phenyl)methane, bis(4-(1′-ethoxypropyloxy)phenyl)methane, 2,2-bis(4′-(2″-tetrahydropyranyloxy))propane, 2,2-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)propane, 2,2-bis(4′-tert-butoxyphenyl)propane, 2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane, 2,2-bis(4-tert-butoxycarbonylmethyloxyphenyl)propane, 2,2-bis(4′-(1″-ethoxyethoxy)phenyl)propane, 2,2-bis(4′-(1″-ethoxypropyloxy)phenyl)propane, tert-butyl 4,4-bis(4′-(2″-tetrahydropyranyloxy)phenyl)-valerate, tert-butyl 4,4-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)-valerate, tert-butyl 4,4-bis(4′-tert-butoxyphenyl)valerate, tert-butyl 4,4-bis(4-tert-butoxycarbonyloxyphenyl)valerate, tert-butyl 4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)-valerate, tert-butyl 4,4-bis(4′-(1″-ethoxyethoxy)phenyl)valerate, tert-butyl 4,4-bis(4′-(1″-ethoxypropyloxy)phenyl)valerate, tris(4-(2′-tetrahydropyranyloxy)phenyl)methane, tris(4-(2′-tetrahydrofuranyloxy)phenyl)methane, tris(4-tert-butoxyphenyl)methane, tris(4-tert-butoxycarbonyloxyphenyl)methane, tris(4-tert-butoxycarbonyloxymethylphenyl)methane, tris(4-(1′-ethoxyethoxy)phenyl)methane, tris(4-(1′-ethoxypropyloxy)phenyl)methane, 1,1,2-tris(4′-(2″-tetrahydropyranyloxy)phenyl)ethane, 1,1,2-tris(4′-(2″-tetrahydrofuranyloxy)phenyl)ethane, 1,1,2-tris(4′-tert-butoxyphenyl)ethane, 1,1,2-tris(4′-tert-butoxycarbonyloxyphenyl)ethane, 1,1,2-tris(4′-tert-butoxycarbonylmethyloxyphenyl)ethane, 1,1,2-tris(4′-(1′-ethoxyethoxy)phenyl)ethane, 1,1,2-tris(4′-(1′-ethoxypropyloxy)phenyl)ethane, tert-butyl cholate, tert-butyl deoxycholate, and tert-butyl lithocholate. The compounds described in JP-A 2003-107706 are also useful.

In the resist composition of the invention, an appropriate amount of the dissolution inhibitor (G) is up to 20 parts, and especially up to 15 parts by weight per 100 parts by weight of the base resin. With more than 20 parts of the dissolution inhibitor, the resist composition becomes less heat resistant because of an increased content of monomer components.

Component C′

The base resin used in the negative working resist composition is (C′) a base resin which is normally alkali soluble, but becomes substantially alkali insoluble under the action of a crosslinker. It is preferably a precursor resin which will be substituted with acid labile groups to form the base resin (C).

Examples of the alkali-soluble resin include poly(p-hydroxystyrene), poly(m-hydroxystyrene), poly(4-hydroxy-2-methylstyrene), poly(4-hydroxy-3-methylstyrene), poly(α-methyl-p-hydroxystyrene), partially hydrogenated p-hydroxystyrene copolymers, p-hydroxystyrene-α-methyl-p-hydroxystyrene copolymers, p-hydroxystyrene-α-methylstyrene copolymers, p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-m-hydroxystyrene copolymers, p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-acrylic acid copolymers, p-hydroxystyrene-methacrylic acid copolymers, p-hydroxystyrene-methyl methacrylate copolymers, p-hydroxystyrene-acrylic acid-methyl methacrylate copolymers, p-hydroxystyrene-methyl acrylate copolymers, p-hydroxystyrene-methacrylic acid-methyl methacrylate copolymers, poly(methacrylic acid), poly(acrylic acid), acrylic acid-methyl acrylate copolymers, methacrylic acid-methyl methacrylate copolymers, acrylic acid-maleimide copolymers, methacrylic acid-maleimide copolymers, p-hydroxystyrene-acrylic acid-maleimide copolymers, and p-hydroxystyrene-methacrylic acid-maleimide copolymers, but are not limited to these combinations.

To impart a certain function, suitable substituent groups may be introduced into some of the phenolic hydroxyl and carboxyl groups on the foregoing polymer (to be protected with acid labile groups). Exemplary and preferred are substituent groups for improving adhesion to the substrate, substituent groups for improving etching resistance, and especially substituent groups which are relatively stable against acid and alkali and effective for controlling such that the dissolution rate in an alkali developer of unexposed and low exposed areas of a resist film may not become too high. Illustrative, non-limiting, substituent groups include 2-hydroxyethyl, 2-hydroxypropyl, methoxymethyl, methoxycarbonyl, ethoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, 4-methyl-2-oxo-4-oxolanyl, 4-methyl-2-oxo-4-oxanyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, acetyl, pivaloyl, adamantyl, isoboronyl, and cyclohexyl. It is also possible to introduce acid-decomposable substituent groups such as tert-butoxycarbonyl and relatively acid-undecomposable substituent groups such as tert-butyl and tert-butoxycarbonylmethyl.

In the resist composition, the resin (C′) is blended in any desired amount, preferably of 65 to 99 parts by weight, especially 65 to 98 parts by weight per 100 parts by weight of the base resin or solids.

Component H

Formulated in the negative resist composition is a crosslinker (F) which forms a crosslinked structure under the action of acid. Typical crosslinkers are compounds having at least two hydroxymethyl, alkoxymethyl, epoxy or vinyl ether groups within a molecule. Substituted glycoluril derivatives, urea derivatives, and hexa(methoxymethyl)melamine compounds are suitable as the crosslinker. Examples include N,N,N′,N′-tetramethoxymethylurea, hexamethoxymethylmelamine, tetraalkoxymethyl-substituted glycoluril compounds such as tetrahydroxymethyl-substituted glycoluril and tetramethoxymethylglycoluril, and condensates of phenolic compounds such as substituted or unsubstituted bis(hydroxymethylphenol) compounds and bisphenol A with epichlorohydrin. Especially preferred crosslinkers are 1,3,5,7-tetraalkoxymethylglycolurils such as 1,3,5,7-tetramethoxymethylglycoluril, 1,3,5,7-tetrahydroxymethylglycoluril, 2,6-dihydroxymethyl-p-cresol, 2,6-dihydroxymethylphenol, 2,2′,6,6′-tetrahydroxymethyl-bisphenol A, 1,4-bis[2-(2-hydroxypropyl)]benzene, N,N,N′,N′-tetramethoxymethylurea, and hexamethoxymethylmelamine.

In the chemically amplified resist composition, an appropriate amount of the crosslinker is, though not limited thereto, 1 to 20 parts, and especially 5 to 15 parts by weight per 100 parts by weight of the base resin. The crosslinkers may be used alone or in admixture of two or more.

In the chemically amplified resist composition of the invention, there may be added such additives as a surfactant for improving coating characteristics, and a light absorbing agent for reducing diffuse reflection from the substrate.

Illustrative, non-limiting, examples of the surfactant include nonionic surfactants, for example, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether, polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenol ether and polyoxyethylene nonylphenol ether, polyoxyethylene polyoxypropylene block copolymers, sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate, and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, and polyoxyethylene sorbitan tristearate; fluorochemical surfactants such as EFTOP EF301, EF303 and EF352 (JEMCO Inc.), Megaface F171, F172, F173, R08 and R30 (Dai-Nippon Ink & Chemicals, Inc.), Fluorad FC430, FC431, FC-4430 and FC-4432 (Sumitomo 3M Co., Ltd.), Aashiguard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfynol E1004, KH-10, KH-20, KH-30 and KH-40 (Asahi Glass Co., Ltd.); organosiloxane polymers KP341, X-70-092 and X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylic acid or methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha Ushi Kagaku Kogyo Co., Ltd.). Inter alia, FC430, Surflon S-381, Surfynol E1004, KH-20 and KH-30 are preferred. These surfactants may be used alone or in admixture.

In the chemically amplified resist composition of the invention, the surfactant is preferably formulated in an amount of up to 2 parts, and especially up to 1 part by weight, per 100 parts by weight of the base resin.

In the chemically amplified resist composition of the invention, a UV absorber may be added. Those UV absorbers described in JP-A 11-190904 are useful, but the invention is not limited thereto. Exemplary UV absorbers are diaryl sulfoxide derivatives such as bis(4-hydroxyphenyl)sulfoxide, bis(4-tert-butoxyphenyl)sulfoxide, bis(4-tert-butoxycarbonyloxyphenyl)sulfoxide, and bis[4-(1-ethoxyethoxy)phenyl]sulfoxide; diarylsulfone derivatives such as bis(4-hydroxyphenyl)sulfone, bis(4-tert-butoxyphenyl)sulfone, bis(4-tert-butoxycarbonyloxyphenyl)sulfone, bis[4-(1-ethoxyethoxy)phenyl]sulfone, and bis[4-(1-ethoxypropoxy)phenyl]sulfone; diazo compounds such as benzoquinonediazide, naphthoquinonediazide, anthraquinonediazide, diazofluorene, diazotetralone, and diazophenanthrone; quinonediazido group-containing compounds such as complete or partial ester compounds between naphthoquinone-1,2-diazido-5-sulfonic acid chloride and 2,3,4-trihydroxybenzophenone and complete or partial ester compounds between naphthoquinone-1,2-diazido-4-sulfonic acid chloride and 2,4,4′-trihydroxybenzophenone; tert-butyl 9-anthracenecarboxylate, tert-amyl 9-anthracenecarboxylate, tert-methoxymethyl 9-anthracenecarboxylate, tert-ethoxyethyl 9-anthracenecarboxylate, 2-tert-tetrahydropyranyl 9-anthracenecarboxylate, and 2-tert-tetrahydrofuranyl 9-anthracenecarboxylate.

The UV absorber may or may not be added to the resist composition depending on the type of resist composition. An appropriate amount of UV absorber, if added, is 0 to 10 parts, more preferably 0.5 to 10 parts, most preferably 1 to 5 parts by weight per 100 parts by weight of the base resin.

For the microfabrication of integrated circuits, any well-known lithography may be used to form a resist pattern from the chemically amplified resist composition of the invention.

The composition is applied onto a substrate (e.g., Si, SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, organic anti-reflective film, etc.) for microfabrication by a suitable coating technique such as spin coating, roll coating, flow coating, dip coating, spray coating or doctor coating. The coating is prebaked on a hot plate at a temperature of 60 to 150° C. for about 1 to 10 minutes, preferably 80 to 140° C. for 1 to 5 minutes. The resulting resist film is generally 0.1 to 2.0 μm thick. Through a photomask having a desired pattern, the resist film is then exposed to radiation, preferably having an exposure wavelength of up to 300 nm, such as UV, deep-UV, electron beam, x-ray, excimer laser light, γ-ray and synchrotron radiation. The preferred light source is a beam from an excimer laser, especially KrF excimer laser, deep UV of 245-255 nm wavelength and ArF excimer laser. The exposure dose is preferably in the range of about 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm². The film is further baked on a hot plate at 60 to 150° C. for 1 to 5 minutes, preferably 80 to 140° C. for 1 to 3 minutes (post-exposure baking=PEB).

Thereafter the resist film is developed with a developer in the form of an aqueous base solution, for example, 0.1 to 5 wt %, preferably 2 to 3 wt % aqueous solution of tetramethylammonium hydroxide (TMAH) for 0.1 to 3 minutes, preferably 0.5 to 2 minutes by conventional techniques such as dip, puddle or spray technique. In this way, a desired resist pattern is formed on the substrate. It is appreciated that the resist composition of the invention is best suited for micro-patterning using such actinic radiation as deep UV with a wavelength of 254 to 193 nm, vacuum UV with a wavelength of 157 nm, electron beam, x-ray, excimer laser light, γ-ray and synchrotron radiation. With any of the above-described parameters outside the above-described range, the process may sometimes fail to produce the desired pattern.

In the practice of the invention, the immersion lithography process involving using ArF excimer laser of 193 nm wavelength and feeding a liquid such as water, glycerin or ethylene glycol between the wafer and the projection lens is advantageously applicable.

EXAMPLE

Synthesis Examples, Examples and Comparative Examples are given below for further illustrating the invention, but they are not to be construed as limiting the invention.

Synthesis Example 1 Synthesis of triphenylsulfonium chloride

Diphenyl sulfoxide, 40 g (0.2 mole), was dissolved in 400 g of dichloromethane, which was stirred under ice cooling. At a temperature below 20° C., 65 g (0.6 mole) of trimethylsilyl chloride was added dropwise to the solution, which was aged for 30 minutes at the temperature. Then, a Grignard reagent which had been prepared from 14.6 g (0.6 mole) of metallic magnesium, 67.5 g (0.6 mole) of chlorobenzene and 168 g of tetrahydrofuran (THF) was added dropwise at a temperature below 20° C. The reaction solution was aged for one hour, after which 50 g of water at a temperature below 20° C. was added to quench the reaction. To this solution, 150 g of water, 10 g of 12N hydrochloric acid, and 200 g of diethyl ether were further added.

The water layer was separated and washed with 100 g of diethyl ether, yielding an aqueous solution of triphenylsulfonium chloride. The compound in aqueous solution form was used in the subsequent reaction without further isolation.

Synthesis Example 2 Synthesis of 4-tert-butylphenyldiphenylsulfonium bromide

The target compound was obtained by following the procedure of Synthesis Example 1 aside from using 4-tert-butylbromobenzene instead of the chlorobenzene in Synthesis Example 1 and increasing the amount of water for extraction.

Synthesis Example 3 Synthesis of 4-tert-butoxyphenyldiphenylsulfonium chloride

The target compound was obtained by following the procedure of Synthesis Example 1 aside from using 4-tert-butoxychlorobenzene instead of the chlorobenzene in Synthesis Example 1, using dichloromethane containing 5 wt % of triethylamine as the solvent, and increasing the amount of water for extraction.

Synthesis Example 4 Synthesis of tris(4-methylphenyl)sulfonium chloride

The target compound was obtained by following the procedure of Synthesis Example 1 aside from using bis(4-methylphenyl)sulfoxide instead of the diphenyl sulfoxide and 4-chlorotoluene instead of the chlorobenzene in Synthesis Example 1, and increasing the amount of water for extraction.

Synthesis Example 5 Synthesis of tris(4-tert-butylphenyl)sulfonium bromide

The target compound was obtained by following the procedure of Synthesis Example 1 aside from using bis(4-tert-butylphenyl)sulfoxide instead of the diphenyl sulfoxide and 4-tert-butylbromobenzene instead of the chlorobenzene in Synthesis Example 1, and increasing the amount of water for extraction.

Synthesis Example 6 Synthesis of bis(4-tert-butylphenyl)iodonium hydrogen sulfate

A mixture of 84 g (0.5 mole) of tert-butylbenzene, 53 g (0.25 mole) of potassium iodate and 50 g of acetic anhydride was stirred under ice cooling, and a mixture of 35 g of acetic anhydride and 95 g of conc. sulfuric acid was added dropwise at a temperature below 30° C. The resulting solution was aged for 3 hours at room temperature and ice cooled again, after which 250 g of water was added dropwise to quench the reaction. The reaction solution was extracted with 400 g of dichloromethane. The organic layer was discolored by adding 6 g of sodium hydrogen sulfite. The organic layer was washed with 250 g of water three times. The washed organic layer was concentrated in vacuum, obtaining a crude target product. The product was used in the subsequent reaction without further purification.

Synthesis Example 7 Synthesis of phenacyltetrahydrothiophenium bromide

88.2 g (0.44 mole) of phenacyl bromide and 39.1 g (0.44 mole) of tetrahydrothiophene were dissolved in 220 g of nitromethane, which was stirred for 4 hours at room temperature. 800 g of water and 400 g of diethyl ether were added to the reaction solution whereupon the mixture separated into two layers. The aqueous layer was taken out, which was an aqueous solution of the target compound, phenacyltetrahydrothiophenium bromide.

Synthesis Example 8 Synthesis of dimethylphenylsulfonium sulfate

6.2 g (0.05 mole) of thioanisole and 6.9 g (0.055 mole) of dimethyl sulfate were stirred for 12 hours at room temperature. 100 g of water and 50 ml of diethyl ether were added to the reaction solution whereupon the mixture separated into two layers. The aqueous layer was taken out, which was an aqueous solution of the target compound, dimethylphenylsulfonium sulfate.

Synthesis Example 9 Synthesis of sodium 2-benzoyloxy-1,1,3,3,3-pentafluoro-propane-1-sulfonate

In 72 g of water was dispersed 10.0 g of 1,1,3,3,3-pentafluoro-2-propan-2-yl benzoate which had been synthesized by a conventional technique. Then 12.0 g of sodium hydrogen sulfite and 1.24 g of benzoyl peroxide were added. Reaction occurred at 85° C. for 65 hours. The reaction solution was allowed to cool, after which toluene was added, followed by separatory operation to separate a water layer. A saturated sodium chloride aqueous solution was added to the water layer whereupon white crystals settled out. The crystals were collected by filtration, washed with a small volume of saturated sodium chloride aqueous solution and then dried in vacuum, obtaining the target compound, sodium 2-benzoyloxy-1,1,3,3,3-pentafluoro-propane-1-sulfonate. White crystals, 5.85 g (yield 43%).

Synthesis Example 10 Synthesis of triphenylsulfonium 2-benzoyloxy-1,1,3,3,3-pentafluoropropane-1-sulfonate

To 50 g of dichloromethane were added an amount (corresponding to 0.011 mole) of the triphenylsulfonium chloride aqueous solution of Synthesis Example 1 and 3.6 g (0.01 mole) of sodium 2-benzoyloxy-1,1,3,3,3-pentafluoro-propane-1-sulfonate synthesized in Synthesis Example 9, followed by stirring. The organic layer was separated and washed with 50 g of water three times. The organic layer was concentrated and 25 g of diethyl ether was added to the residue for crystallization. The crystals were filtered and dried, obtaining the target compound. White crystals, 4.5 g (yield 75%).

Synthesis Example 11 Synthesis of triphenylsulfonium 2-hydroxy-1,1,3,3,3-pentafluoropropane-1-sulfonate (PAG1)

In 72 g of methanol was dissolved 34.4 g of triphenylsulfonium 2-benzoyloxy-1,1,3,3,3-pentafluoropropane-1-sulfonate synthesized in Synthesis Example 10. While stirring under ice cooling, 54.0 g of a 5% sodium hydroxide aqueous solution was added dropwise to the solution at a temperature below 10° C. The reaction solution was aged at the temperature for 4 hours. At a temperature below 10° C., 6.8 g of 12N hydrochloric acid was added to quench the reaction. The methanol was distilled off under vacuum, and 270 g of dichloromethane was added. The organic layer was washed with 40 g of water three times. The organic layer was then concentrated and 60 g of diethyl ether was added to the residue for crystallization. The crystals were filtered and dried, obtaining the target compound. White crystals, 24.3 g (yield 85%).

The target compound was analyzed by spectroscopy. The data of IR spectroscopy are shown below. The NMR spectra, ¹H-NMR (300 MHz in DMSO-d₆) and ¹⁹F-NMR (282 MHz in DMSO-d₆ (shift standard CF₃CO₂D)) are shown in FIGS. 1 and 2.

Infrared absorption spectra (IR, KBr, cm⁻¹)

3278, 3064, 1722, 1479, 1448, 1367, 1261, 1234, 1211, 1172, 1124, 1106, 1070, 987, 823, 755, 746, 684, 644, 503

Time-of-flight mass spectrometry (TOFMS; MALDI)

POSITIVE M⁺263 (corresponding to (C₆H₅)₃S⁺)

NEGATIVE M⁻229 (corresponding to CF₃CH(OH)CF₂SO₃ ⁻)

Synthesis Examples 12-18

Target compounds were synthesized as in Synthesis Examples 10 and 11 except that the sulfonium salts prepared in Synthesis Examples 2 to 8 were used. The resulting onium salts PAG2 to PAG8 are shown below.

They were analyzed by spectroscopy. The NMR spectra, ¹H-NMR (300 MHz in DMSO-d₆) and ¹⁹F-NMR (282 MHz in DMSO-d₆ (shift standard CF₃CO₂D)) of PAG2 are shown in FIGS. 3 and 4.

Synthesis Example 19 Synthesis of sodium 2-hydroxy-1,1,3,3,3-pentafluoro-propane-1-sulfonate (Anion 1)

In 43 g of water was dissolved 14.6 g of sodium 2-benzoyloxy-1,1,3,3,3-pentafluoro-propane-1-sulfonate synthesized in Synthesis Example 9. The solution was stirred under ice cooling. To the solution, 7.4 g of a 26% sodium hydroxide aqueous solution was added dropwise at a temperature below 10° C. The reaction solution was aged for 1 hour at the temperature and for a further 1 hour at room temperature. The solution was washed with toluene, from which an aqueous layer was separated. It was an aqueous solution of the target compound, sodium 2-hydroxy-1,1,3,3,3-pentafluoropropane-1-sulfonate. Without further isolation, the aqueous solution was directly analyzed by NMR spectroscopy and TOFMS for confirming the formation of the target compound.

The spectroscopic data of the compound are shown below. The NMR spectrum, ¹⁹F-NMR (282 MHz in D₂O (shift standard CF₃CO₂D)) is shown in FIG. 5.

Time-of-flight mass spectrometry (TOFMS; MALDI)

NEGATIVE M⁻229 (corresponding to CF₃CH(OH)CF₂SO₃ ⁻)

Reference Example 1 Synthesis of triphenylsulfonium 2-acetoxy-1,1,3,3,3-pentafluoropropane-1-sulfonate (PAG9)

In 28 g of methylene chloride were dissolved 3.0 g of triphenylsulfonium 2-hydroxy-1,1,3,3,3-pentafluoropropane-1-sulfonate synthesized in Synthesis Example.11 and 0.7 g of pyridine. While stirring under ice cooling, 0.8 g of acetic anhydride was added to the solution. Thereafter, 0.7 g of triethylamine and 0.04 g of 4-(N,N-dimethylamino)pyridine were added to the solution, which was stirred for 4 hours. Water, 20 g, was added to quench the reaction. The organic layer was separated and washed with 20 g of water three times. The organic layer was then concentrated, obtaining triphenylsulfonium 2-acetoxy-1,1,3,3,3-pentafluoropropane-1-sulfonate. Colorless oily matter, 2.2 g (yield 70%).

The target compound was analyzed by spectroscopy. The data of IR spectroscopy are shown below. The NMR spectra, ¹H-NMR (300 MHz in DMSO-d₆) and ¹⁹F-NMR (282 MHz in DMSO-d₆ (shift standard CF₃CO₂D)) are shown in FIGS. 6 and 7.

Infrared absorption spectra (IR, KBr, cm⁻¹)

3089, 3064, 2971, 1779, 1581, 1477, 1448, 1373, 1322, 1253, 1213, 1186, 1164, 1116, 1091, 1072, 995, 919, 750, 684, 642

Examples 1-16 & Comparative Examples 1-3 Evaluation of Resist Resolution

Resist compositions were prepared by dissolving the photoacid generators of Synthesis Examples, Polymers 1 to 8 as the base resin, dissolution accelerator DRR1, dissolution inhibitor DRI1, and basic compound in a solvent containing 0.01 wt % of surfactant FC-430 (Sumitomo 3M Co., Ltd.) according to the formulation shown in Tables 1 and 2. They were filtered through a Teflon® filter having a pore size of 0.2 μm, giving resist solutions. Polymers 1 to 8, DRR1 and DRI1 are shown below.

An antireflective coating liquid ARC-29A (Nissan Chemical Co., Ltd.) was coated onto a silicon substrate and baked at 200° C. for 60 seconds to form an antireflective coating of 78 nm thick. The resist solution was spin coated onto the antireflective coating and baked on a hot plate at 120° C. for 60 seconds, forming a resist film of 200 nm thick. The resist film was exposed by means of an ArF excimer laser microstepper model S305B (Nikon Corp., NA 0.68, ⅔ annular illumination, Cr mask), post-exposure baked (PEB) at 110° C. for 90 seconds, and developed with a 2.38 wt % aqueous solution of tetramethylammonium hydroxide (TMAH) for 60 seconds.

An optimal exposure dose (sensitivity Eop, mJ/cm²) was the exposure which provided a 1:1 resolution at the top and bottom of a 0.12-μm group line-and-space pattern. The minimum line width (μm) of a line-and-space pattern which was ascertained separate at this dose was the resolution of a test resist. The profile of the resist pattern as resolved was evaluated by observing a cross section of the resist under a scanning electron microscope. The formulation and test results of the resist compositions are shown in Tables 1 and 2.

The solvents and basic compounds in Tables 1 and 2 are shown below as well as the photoacid generators in Comparative Examples.

Solvent A: propylene glycol monomethyl ether acetate

-   -   Solvent B: cyclohexanone     -   Basic Compound A: tri-n-octylamine     -   Basic Compound B: triethanolamine     -   Basic Compound C: trismethoxymethoxyethylamine     -   Basic Compound D: tris(2-acetoxyethyl)amine     -   TPS-NfO: triphenylsulfonium perfluoro-1-butanesulfonate     -   TPS-PFOS: triphenylsulfonium perfluoro-1-octanesulfonate

TABLE 1 Formulation Example (pbw) 1 2 3 4 5 6 7 8 9 10 Polymer 1 80 80 Polymer 2 80 80 Polymer 3 80 Polymer 4 80 Polymer 5 80 Polymer 6 80 Polymer 7 80 Polymer 8 80 PAG1 4 4 4 4 4 4 4 4 PAG2 5 PAG3 5 PAG4 PAG5 PAG6 TPS-NfO TPS-PFOS Basic Compound A 0.5 0.5 0.5 0.5 Basic Compound B 0.5 0.5 0.5 Basic Compound C 0.5 0.5 0.5 Basic Compound D DRR1 DRI1 Solvent A 800 800 800 800 800 800 800 800 800 Solvent B 800 Tests Sensitivity (mJ/cm²) 23 22 23 24 25 22 22 21 32 34 Resolution (μm) 0.11 0.11 0.11 0.11 0.12 0.10 0.11 0.11 0.11 0.12

TABLE 2 Formulation Example Comparative Example (pbw) 11 12 13 14 15 16 1 2 3 Polymer 1 40 80 Polymer 2 40 40 60 80 80 40 Polymer 3 40 40 Polymer 4 40 80 Polymer 5 40 20 Polymer 6 Polymer 7 Polymer 8 PAG1 4 PAG2 4 PAG3 5 PAG4 6 PAG5 6 PAG6 6 TPS-NfO 1 4 2 TPS-PFOS 1 4 3 Basic Compound A 0.5 0.5 0.5 Basic Compound B Basic Compound C 0.5 0.5 0.5 Basic Compound D 0.5 0.5 0.5 DRR1 10 DRI1 10 Solvent A 600 800 800 800 800 800 800 800 800 Solvent B 200 Tests Sensitivity (mJ/cm²) 35 37 38 42 24 33 26 30 28 Resolution (μm) 0.11 0.11 0.11 0.12 0.11 0.11 0.11 0.11 0.11

Next, simulative immersion photolithography was carried out using the resist compositions of Examples 1, 4, 9 and Comparative Example 1. Specifically, a resist film of 125 nm thick was formed on a wafer by a procedure as described above and exposed by means of an ArF excimer laser microstepper model S307E (Nikon Corp., NA 0.85, dipole). Immediately after the exposure, deionized water was fed over the entire surface of the wafer, whereby the exposed surface of resist was immersed in deionized water for 60 seconds (puddle). The wafer was rotated to spin off the water, followed by ordinary PEB and development. The number of defects in the pattern formed after development was counted by a wafer inspection system WINWIN 50-1200L (Tokyo Seimitsu Co., Ltd.). A defect density was computed therefrom.

-   -   Defect density (/cm²)=(total number of detected defects)/(test         area).     -   Pattern formed: repetitive pattern of 80 nm pitch, 160 nm         line-and-space     -   Defect detection: light source UV, detection pixel size 0.125         μm, cell-to-cell mode

Additionally, the pattern profile in resist cross-section was observed under a scanning electron microscope. The results are shown in Table 3.

TABLE 3 Defect density Pattern profile (/cm²) Example 1 rectangular ≦0.05 Example 4 rectangular ≦0.05 Example 9 rectangular ≦0.05 Comparative extreme T-top 10 Example 1

As is evident from Tables 1 to 3, the resist compositions of the invention have a high sensitivity and high resolution and invite neither profile changes nor defects during a long term of water rinsing as compared with the prior art composition, suggesting an ability to comply with the immersion photolithography. As demonstrated in Reference Example 1, the photoacid generator capable of generating a sulfonic acid having formula (1) is useful as an intermediate for synthesis because the hydroxyl group in the molecule can be converted into a bulkier functional group.

Japanese Patent Application No. 2005-316156 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A sulfonate salt having the general formula (1a): CF₃—CH(OH)—CF₂SO₃ ⁻M⁺  (1a) wherein M⁺ is a lithium, sodium, potassium, ammonium or tetramethylammonium ion.
 2. A photoacid generator for chemically amplified resist compositions which generates a sulfonic acid upon exposure to high-energy radiation selected from UV, deep-UV, electron beam, x-ray, excimer laser, gamma-ray and synchrotron radiation, said sulfonic acid having the general formula (1): CF₃—CH(OH)—CF₂SO₃ ⁻H⁺  (1).
 3. A sulfonium salt having the general formula (2): R¹R²R³S⁺ CF₃—CH(OH)—CF₂SO₃ ⁻  (2) wherein R¹, R² and R³ are each independently selected from the class consisting of substituted or unsubstituted, straight or branched C₁-C₁₀ alkyl, alkenyl and oxoalkyl groups, and substituted or unsubstituted C₆-C₈ aryl, aralkyl and aryloxoalkyl groups, or any two or more of R¹, R² and R³ may bond together to form a ring with the sulfur atom.
 4. A sulfonium salt having the general formula (2a): (R⁴—(O)_(n))_(m)-PhS⁺Ph₂ CF₃—CH(OH)—CF₂SO₃ ⁻  (2a) wherein R⁴ is a substituted or unsubstituted, straight, branched or cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or unsubstituted C₆-C₁₄ aryl group, Ph is phenyl, m is 1 to 5, and n is 0 or
 1. 5. A iodonium salt having the general formula (2b): R⁴—(O)_(n)-PhI⁺Ph(O)_(n)—R⁴ CF₃—CH(OH)—CF₂SO₃ ⁻  (2b) wherein R⁴ is a substituted or unsubstituted, straight, branched or cyclic C₁-C₂₀ alkyl or alkenyl group or a substituted or unsubstituted C₆-C₁₄ aryl group, Ph is phenyl, and n is 0 or
 1. 6. A N-sulfonyloxyimide compound having the general formula (3a):

wherein X and Y are each independently hydrogen or a substituted or unsubstituted C₁-C₆ alkyl group, or X and Y may bond together to form a saturated or unsaturated C₆-C₁₂ ring with the carbon atoms to which they are attached, and Z is a single bond, double bond, methylene group or oxygen atom.
 7. An oxime sulfonate compound having the general formula (3b):

wherein q is 0 or 1, p is a single bond, a substituted or unsubstituted C₁-C₂₀ alkyl group or a substituted or unsubstituted C₆-C₁₅ aryl group when q is 0, or p is a substituted or unsubstituted C₁-C₂₀ alkylene group or a substituted or unsubstituted C₆-C₁₅ arylene group when q is 1, EWG is a cyano, trifluoromethyl, perfluoroethyl, perfluoropropyl, 5H-perfluoropentyl, 6H-perfluorohexyl, nitro or methyl group, and when q is 1, two EWG's may bond together to form a ring of 6 carbon atoms with the carbon atoms to which they are attached.
 8. A resist composition comprising a base resin, an acid generator, and a solvent, said acid generator comprising a photoacid generator which generates a sulfonic acid having formula (1) as set forth in claim
 2. 9. The resist composition of claim 8, wherein said base resin is at least one polymer selected from the group consisting of poly(meth)acrylic acid and derivatives thereof, alternating copolymers of a cycloolefin derivative and maleic anhydride, copolymers of ternary or more components comprising a cycloolefin derivative, maleic anhydride, and polyacrylic acid or derivatives thereof, cycloolefin derivative-α-trifluoromethyl acrylate copolymers, polynorbornene, ring-opening metathesis polymers, and hydrogenated ring-opening metathesis polymers.
 10. The resist composition of claim 8, wherein said base resin is a polymeric structure containing silicon atoms.
 11. The resist composition of claim 8, wherein said base resin is a polymeric structure containing fluorine atoms.
 12. A chemically amplified positive resist composition comprising a base resin as set forth in claim 9, a photoacid generator which generates a sulfonic acid having formula (1) and a solvent, wherein said base resin is insoluble or substantially insoluble in a liquid developer, and becomes soluble under the action of the acid.
 13. The chemically amplified positive resist composition of claim 12, further comprising a basic compound.
 14. The chemically amplified positive resist composition of claim 12, further comprising a dissolution inhibitor.
 15. A process for forming a pattern comprising the steps of: applying the resist composition of claim 8 onto a substrate to form a coating, heat treating the coating and exposing it to high-energy radiation having a wavelength of up to 300 nm through a photomask, and optionally heat treating and developing the exposed coating with a developer.
 16. The process of claim 15, wherein the exposing step relies on immersion lithography comprising directing radiation from an ArF excimer laser having a wavelength of 193 nm through a projection lens, with a liquid such as water, glycerin or ethylene glycol intervening between the coated substrate and the projection lens. 